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Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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22 Feb 2012, 18:59
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Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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22 Feb 2012, 21:02
Is x > 0?(1) \(x+3=4x3\) > LHS is an absolute value, which is always nonnegative (\(some \ expression\geq{0}\)), so RHS must also be nonnegative > \(4x3\geq{0}\) > \(x\geq{\frac{3}{4}}\), hence \(x>0\). Sufficient. You can see here that you don't even need to find exact value(s) of x to answer the question. (2) \(x3=2x3\). Square both sides: \((x3)^2=(2x3)^2\) > \((2x3)^2(x3)^2=0\). Apply \(a^2b^2=(ab)(a+b)\), rather than squaring: > \(x(3x6)=0\) > \(x=0\) or \(x=2\). Not sufficient. Answer: A. Hope it helps.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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25 Feb 2012, 09:45
Bunnel, For statement one, I understand that you have not solved for x in your solution. I am still learning the abs value and in equalities. Can you share your thoughts on the following solution (solving for x in both statements)
a. x+3 = 4x 3 x+3 = x + 3 for x + 3 >= 0 > x > 3. Solving for x, x + 3 = 4x 3 > 6 = 3x > x = 2 ( solution accepted since x > 3)
 x + 3 = (x +3 ) for x + 3 < 0 > x < 3. Solving for x, x  3 = 4x 3 5x = 0 > x = 0 ( solution discarded as x is not < 3)
A is sufficient.
b. x 3 = 2x 3 x 3 = x 3 for x3 >= 0 > x >= 3 x 3 = (x 3) for x3 < 0 > x < 3
2x 3  = 2x 3 for 2x 3 >= 0 > x >=3/2 2x 3  = (2x 3) for 2x 3 < 0 > x < 3/2
So we have 3 ranges
1) x >=3 ==> x  3 = 2x 3 ====> x = 0 ; discard 2) 3/2 < x < 3 ===> (x3) = 2x 3 ====> x + 3 = 2x 3 ===> x =2 ( accepted solution ) 3) x < 3/2 ===> (x3) = (2x 3) ====> x = 3 (discarded the solution)
Let me know if I have solved the question correctly. I know the process is lengthy.
One more question, if we consider the only acceptable solution in statement b i.e., x =2 (case 3/2 < x < 3), then both statements are sufficient independently and we get the answer as option (D).
Please discuss.
Regards




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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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25 Feb 2012, 09:52
saxenaashi wrote: Bunnel, For statement one, I understand that you have not solved for x in your solution. I am still learning the abs value and in equalities. Can you share your thoughts on the following solution (solving for x in both statements)
a. x+3 = 4x 3 x+3 = x + 3 for x + 3 >= 0 > x > 3. Solving for x, x + 3 = 4x 3 > 6 = 3x > x = 2 ( solution accepted since x > 3)
 x + 3 = (x +3 ) for x + 3 < 0 > x < 3. Solving for x, x  3 = 4x 3 5x = 0 > x = 0 ( solution discarded as x is not < 3)
A is sufficient.
b. x 3 = 2x 3 x 3 = x 3 for x3 >= 0 > x >= 3 x 3 = (x 3) for x3 < 0 > x < 3
2x 3  = 2x 3 for 2x 3 >= 0 > x >=3/2 2x 3  = (2x 3) for 2x 3 < 0 > x < 3/2
So we have 3 ranges
1) x >=3 ==> x  3 = 2x 3 ====> x = 0 ; discard 2) 3/2 < x < 3 ===> (x3) = 2x 3 ====> x + 3 = 2x 3 ===> x =2 ( accepted solution ) 3) x < 3/2 ===> (x3) = (2x 3) ====> x = 3 (discarded the solution)
Let me know if I have solved the question correctly. I know the process is lengthy.
One more question, if we consider the only acceptable solution in statement b i.e., x =2 (case 3/2 < x < 3), then both statements are sufficient independently and we get the answer as option (D).
Please discuss.
Regards It seems that you understand this method very well. Everything is correct except the red parts: (x3) = (2x 3) > x=0 (not x=3), so it's also a valid solution. Hence for (2) you have two valid solutions x=2 and x=0 (just like in my post above), which makes this statement not sufficient. Hope it's clear.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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17 Apr 2012, 05:19
dvinoth86 wrote: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3 Liked the question? encourage by giving kudos Remember: When you have  on both sides of eqn you do not need to VERIFY the answer by putting them back in eqn BUT when you have  on only one side you MUST VERIFY the answer by putting them back in eqn(1) x + 3 = 4x – 3 a) x + 3 = 4x – 3 => x=2 .. VALID b) (x + 3) = 4x – 3 => x=0 .. INVALID Hence Sufficient (2) x – 3 = 2x – 3 => x = 0 or 6 .. INVALID Hence InSufficient



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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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04 Jun 2013, 07:00
WholeLottaLove wrote: Hi! Why do we not find the positive and negative values for x+3=4x3? Is it because this isn't a <, >, >= problem? Thanks! Bunuel wrote: Is x > 0?
(1) \(x+3=4x3\) > LHS is an absolute value, which is always nonnegative (\(some \ expression\geq{0}\)), so RHS must also be nonnegative > \(4x3\geq{0}\) > \(x\geq{\frac{3}{4}}\), hence \(x>0\). Sufficient. You can see here that you don't even need to find exact value(s) of x to answer the question.
(2) \(x3=2x3\). Square both sides: \((x3)^2=(2x3)^2\) > \((2x3)^2(x3)^2=0\). Apply \(a^2b^2=(ab)(a+b)\), rather than squaring: > \(x(3x6)=0\) > \(x=0\) or \(x=2\). Not sufficient.
Answer: A.
Hope it helps. One can do this way too, but the way shown in my post is faster.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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12 May 2015, 22:57
ranaazad wrote: vikram4689 wrote: dvinoth86 wrote: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3 Liked the question? encourage by giving kudos Remember: When you have  on both sides of eqn you do not need to VERIFY the answer by putting them back in eqn BUT when you have  on only one side you MUST VERIFY the answer by putting them back in eqn(1) x + 3 = 4x – 3 a) x + 3 = 4x – 3 => x=2 .. VALID b) (x + 3) = 4x – 3 => x=0 .. INVALID Hence Sufficient (2) x – 3 = 2x – 3 => x = 0 or 6 .. INVALID Hence InSufficient Your statement 1 has two sceneries. Then how does it become sufficient? Dear ranaazadThe solution quoted by you above has some tacit steps. I'll list them here: St. 1 says: x + 3 = 4x – 3 . . . (1) Case 1: x + 3 > = 0That is, x > = 3 In this case, x+3 = (x+3) So, Equation 1 becomes: x + 3 = 4x  3 => 6 = 3x => x = 2 Does this value of x satisfy the condition of Case 1, that x > = 3? Yes, it does. So, x = 2 is a valid value of x. Let's now consider Case 2: x + 3 < 0That is, x < 3 In this case, x+3 = (x+3) So, Equation 1 becomes: (x + 3) = 4x  3 => x  3 = 4x  3 => 0 = 5x => x = 0 Does this value of x satisfy the condition of Case 2, that x < 3? No, it doesn't. So, x = 0 is an INVALID value of x. Thus, we got only 1 valid value of X from Statement 1 (x = 2) and so, Statement 1 is sufficient to say that x > 0. Hope this answered your doubt! Japinder
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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29 Dec 2019, 10:56
Quote: Hi
I am not clear why are we taking ONLY x+3 as x+3>=0 and not x+3<=0? Whenever you translate an absolute value to 'go both ways' like in that explanation, you need to take an additional step and double check to make sure you haven't come up with an invalid solution. You're correct that you need to consider both x + 3 > 0 and x + 3 < 0. But once you've figured out what that implies about the value of x, double check by plugging x back in. For instance, if x + 3 < 0, we ended up figuring out that x has to equal 0. But that's impossible, because 0 + 3 isn't less than 0. So, we didn't get a valid solution at all, and only the x + 3 > 0 solution worked.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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25 Feb 2012, 10:15
saxenaashi wrote: Works. Thanks for pointing out the mistake and quick response too. I am just learning this so working ground up, hence I am not hesitant in taking long route initially. After next few questions, I would be tuned to extract the ranges I guess. Is there a condition on squaring the sides of the equation or inequation. Regards A. We can raise both parts of an inequality to an even power if we know that both parts of an inequality are nonnegative (the same for taking an even root of both sides of an inequality).For example: \(2<4\) > we can square both sides and write: \(2^2<4^2\); \(0\leq{x}<{y}\) > we can square both sides and write: \(x^2<y^2\); But if either of side is negative then raising to even power doesn't always work. For example: \(1>2\) if we square we'll get \(1>4\) which is not right. So if given that \(x>y\) then we can not square both sides and write \(x^2>y^2\) if we are not certain that both \(x\) and \(y\) are nonnegative. B. We can always raise both parts of an inequality to an odd power (the same for taking an odd root of both sides of an inequality).For example: \(2<1\) > we can raise both sides to third power and write: \(2^3=8<1=1^3\) or \(5<1\) > \(5^2=125<1=1^3\); \(x<y\) > we can raise both sides to third power and write: \(x^3<y^3\). So in statement (2) since both parts of expression are nonnegative we can safely apply squaring. Hope it helps.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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27 Feb 2012, 22:30
terance wrote: Well, I have a little bit another solution for this problem Consider (1): if x>3 then x+3=4x3, so x=2, sufficient if x<3, then x3=4x3, which Leeds to answer x=0, which is wrong because we consider only x<3 Sum up (1) is sufficient The saim logic can be applied to the (2), and it is possible to derive that (2) is sufficient So the answer is D either (1) is sufficient or (2) is sufficient In your logic, you gave a mistake, because you've missed the root. Posted from GMAT ToolKitWelcome to GMAT Club. Unfortunately your answer is not correct: OA for this question is A, not D (you can see it under the spoiler in the initial post). (2) x – 3 = 2x – 3 has two roots x=0 and x=2 (just substitute these values to see that they both satisfy the given equation), so you can not get the single numerical value of x, which makes this statement insufficient. You can refer to above solutions for two different approaches of how to get these roots for (2). Please ask if anything remains unclear.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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10 May 2013, 01:01
nikhil007 wrote: Hi Bunuel This is how I solved the 2 statements, http://campl.us/fWdgqiT5EsKand I get 0 & 2 for both statements, can u tell me what wrong am I doing? Posted from my mobile device If you substitute x=0 in x + 3 = 4x – 3 you'll get: LHS=x + 3=3 and RHS=4x – 3=3, thus \(LHS\neq{RHS}\), which means that x=0 is not the root of the given equation. When expanding x+3: When x<3, then x+3=(x+3), so in this case we'll have (x+3)=4x3 > x=0 > discard this value since 0 is not less than 3 (we consider the range when x<3). When x>=3, then x+3=x+3, so in this case we'll have x+3=4x3 > x=2 > this value of x is OK since 2>3. So, x + 3 = 4x  3 has only one root, x=2. Hope it's clear.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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04 Jun 2013, 08:13
WholeLottaLove wrote: Bunuel wrote: \(x+3=4x3\). Check point is at \(x=3\) (check point, is the value of x for which the value of an expression in modulus equals to zero).
When \(x\leq{3}\), then \(x+3<0\), thus \(x+3=(x+3)\). So, in this case we have \((x+3)=4x3\) > \(x=0\) > discard this solution since we consider the range when \(x\leq{3}\).
When \(x>{3}\), then \(x+3>0\), thus \(x+3=x+3\). So, in this case we have \(x+3=4x3\) > \(x=2\) > since \(x=2>3\), then this solution is valid.
So, we have that \(x+3=4x3\) has only one root: \(x=2\).
Hope it's clear. Why do we discard that solution? We consider the range \(x\leq{3}\). x=0 is out of this range. Check absolute values chapter of math book: mathabsolutevaluemodulus86462.htmlHope it helps.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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03 Aug 2018, 22:07
Mo2men wrote: Thanks GMATGuruNY. In this type of questions asking for sign of x, does this mean that I can deal with such statement in same manner like statement 1? or do I need open modulus to be sure from the sign? Since the question stem asks whether x>0  and an equation with absolute value on both sides can have both a positive and a nonpositive solution  I recommend that you solve the equation, either by opening up the modulus or by squaring both sides.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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28 Nov 2018, 05:38
topper97 wrote: Bunuel does it mean that in all questions based on absolute values, one solution of it would be 0? I'm clear with Stat1 but in stat 2, I used the formula by squaring both sides of absolute figures to find the inequality range. Here is what I did. x−3=2x−3 Square both sides: (x−3)^2=(2x−3)^2 x^26x+9=4x^212x+9 3x^2=6x Therefore, x=2. So I chose option D. Can you help me to find what is the error? I'm not getting it. All I did was use the formula. 1. Of course 0 is NOT a solution of all absolute value questions. Why would it be? 2. You solved 3x^2 = 6x incorrectly. You cannot reduce 3x^2 = 6x by x because x can be 0 and we cannot divide by 0. By doing so you loose a root, namely x = 0. Never reduce equation by variable (or expression with variable), if you are not certain that variable (or expression with variable) doesn't equal to zero. We cannot divide by zero.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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25 Feb 2012, 10:07
Bunuel wrote: saxenaashi wrote: Bunnel, For statement one, I understand that you have not solved for x in your solution. I am still learning the abs value and in equalities. Can you share your thoughts on the following solution (solving for x in both statements)
a. x+3 = 4x 3 x+3 = x + 3 for x + 3 >= 0 > x > 3. Solving for x, x + 3 = 4x 3 > 6 = 3x > x = 2 ( solution accepted since x > 3)
 x + 3 = (x +3 ) for x + 3 < 0 > x < 3. Solving for x, x  3 = 4x 3 5x = 0 > x = 0 ( solution discarded as x is not < 3)
A is sufficient.
b. x 3 = 2x 3 x 3 = x 3 for x3 >= 0 > x >= 3 x 3 = (x 3) for x3 < 0 > x < 3
2x 3  = 2x 3 for 2x 3 >= 0 > x >=3/2 2x 3  = (2x 3) for 2x 3 < 0 > x < 3/2
So we have 3 ranges
1) x >=3 ==> x  3 = 2x 3 ====> x = 0 ; discard 2) 3/2 < x < 3 ===> (x3) = 2x 3 ====> x + 3 = 2x 3 ===> x =2 ( accepted solution ) 3) x < 3/2 ===> (x3) = (2x 3) ====> x = 3 (discarded the solution)
Let me know if I have solved the question correctly. I know the process is lengthy.
One more question, if we consider the only acceptable solution in statement b i.e., x =2 (case 3/2 < x < 3), then both statements are sufficient independently and we get the answer as option (D).
Please discuss.
Regards It seems that you understand this method very well. Everything is correct except the red parts: (x3) = (2x 3) > x=0 (not x=3), so it's also a valid solution. Hence for (2) you have two valid solutions x=2 and x=0 (just like in my post above), which makes this statement not sufficient. Hope it's clear. Works. Thanks for pointing out the mistake and quick response too. I am just learning this so working ground up, hence I am not hesitant in taking long route initially. After next few questions, I would be tuned to extract the ranges I guess. Is there a condition on squaring the sides of the equation or inequation. Regards



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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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27 Feb 2012, 22:09
Well, I have a little bit another solution for this problem Consider (1): if x>3 then x+3=4x3, so x=2, sufficient if x<3, then x3=4x3, which Leeds to answer x=0, which is wrong because we consider only x<3 Sum up (1) is sufficient The saim logic can be applied to the (2), and it is possible to derive that (2) is sufficient So the answer is D either (1) is sufficient or (2) is sufficient In your logic, you gave a mistake, because you've missed the root. Posted from GMAT ToolKit



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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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09 May 2013, 12:38
Hi Bunuel This is how I solved the 2 statements, http://campl.us/fWdgqiT5EsKand I get 0 & 2 for both statements, can u tell me what wrong am I doing? Posted from my mobile device



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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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04 Jun 2013, 06:56
Hi! Why do we not find the positive and negative values for x+3=4x3? Is it because this isn't a <, >, >= problem? Thanks! Bunuel wrote: Is x > 0?
(1) \(x+3=4x3\) > LHS is an absolute value, which is always nonnegative (\(some \ expression\geq{0}\)), so RHS must also be nonnegative > \(4x3\geq{0}\) > \(x\geq{\frac{3}{4}}\), hence \(x>0\). Sufficient. You can see here that you don't even need to find exact value(s) of x to answer the question.
(2) \(x3=2x3\). Square both sides: \((x3)^2=(2x3)^2\) > \((2x3)^2(x3)^2=0\). Apply \(a^2b^2=(ab)(a+b)\), rather than squaring: > \(x(3x6)=0\) > \(x=0\) or \(x=2\). Not sufficient.
Answer: A.
Hope it helps.



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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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04 Jun 2013, 07:26
Hmmm... When I solve for the pos. and neg. values of x+3=4x3 I get: I. x+3=4x3 ==> 3x=6 ==> x=2II. x+3=(4x3) ==> x+3=4x+3 ==> 5x=0 ==> x=0So here in my presumably incorrect simplification, I have x=2 and x=0 in which case we can't be sure if x>0 For many abs. value questions it seems that you have to find the positive and negative cases each equation. I get that in this case, x+3=4x3 means that 4x3 is positive but why for other, similar questions, is solving for the positive and negative cases necessary? Bunuel wrote: WholeLottaLove wrote: Hi! Why do we not find the positive and negative values for x+3=4x3? Is it because this isn't a <, >, >= problem? Thanks! Bunuel wrote: Is x > 0?
(1) \(x+3=4x3\) > LHS is an absolute value, which is always nonnegative (\(some \ expression\geq{0}\)), so RHS must also be nonnegative > \(4x3\geq{0}\) > \(x\geq{\frac{3}{4}}\), hence \(x>0\). Sufficient. You can see here that you don't even need to find exact value(s) of x to answer the question.
(2) \(x3=2x3\). Square both sides: \((x3)^2=(2x3)^2\) > \((2x3)^2(x3)^2=0\). Apply \(a^2b^2=(ab)(a+b)\), rather than squaring: > \(x(3x6)=0\) > \(x=0\) or \(x=2\). Not sufficient.
Answer: A.
Hope it helps. One can do this way too, but the way shown in my post is faster.



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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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04 Jun 2013, 07:42
\(x+3=4x3\). Check point is at \(x=3\) (check point, is the value of x for which the value of an expression in modulus equals to zero). When \(x\leq{3}\), then \(x+3<0\), thus \(x+3=(x+3)\). So, in this case we have \((x+3)=4x3\) > \(x=0\) > discard this solution since we consider the range when \(x\leq{3}\). When \(x>{3}\), then \(x+3>0\), thus \(x+3=x+3\). So, in this case we have \(x+3=4x3\) > \(x=2\) > since \(x=2>3\), then this solution is valid. So, we have that \(x+3=4x3\) has only one root: \(x=2\). Hope it's clear.
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Re: Is x > 0? (1) x + 3 = 4x – 3 (2) x – 3 = 2x – 3
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