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The line represented by the equation y = 4 – 2x is the [#permalink]
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18 Feb 2012, 18:55
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The line represented by the equation y = 4 – 2x is the perpendicular bisector of line segment RP. If R has the coordinates (4, 1), what are the coordinates of point P? (A) (–4, 1) (B) (–2, 2) (C) (0, 1) (D) (0, –1) (E) (2, 0) How come the answer will be D? This is how I am trying to solve this.
First, rewrite the line y=42x as y = 2x+4 The equation is now in the form y = mx+b where m represents the slope and b represents the yintercept.Thus, the slope of this line is 2. By definition, if a line is the perpendicular bisector of any line, the slope of line which is perpendicular bisector is the negative inverse of the slope of line G. Since we are told that the line y = 2x+4 is the perpendicular bisector of line segment RP, line segment RP must have a slope of \(\frac{1}{2}\) (which is the negative inverse of slope of line y). Now we know that the slope of the line containing segment RP is\(\frac{1}{2}\) but we do not know its yintercept. We can write the equation of this line as , y = 1/2x+b, where b represents the unknown yintercept. To solve for b, we can use the given information that the coordinates of point R are (4, 1). Since point R is on the line y = 1/2x+b, we can plug 4 in for x and 1 in for y to get b = 1 Therefore, equation of line RP will become y = 1/2x1 Also , y = 2x +4 (Equation of perpendicular bisector) (2)
Equating the two we will get x =2 . Putting this value of x in we get y = 0.
So the points should be (2,0) i.e. answer E.
Where I am getting this wrong guys?
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Re: Coordinates of Point P [#permalink]
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18 Feb 2012, 19:12
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The line represented by the equation y = 4 – 2x is the perpendicular bisector of line segment RP. If R has the coordinates (4, 1), what are the coordinates of point P? A. (–4, 1) B. (–2, 2) C. (0, 1) D. (0, –1) E. (2, 0) Again, there is no need of equations to solve this question. Plot the line y = 4 – 2x (just find the x and y intercepts and draw the line through them): Attachment:
Bisector.png [ 16 KiB  Viewed 21834 times ]
Now, it's easy to SEE that no blue point can be the mirror reflection of R around the line but (0, 1). Answer: D. P.S. Answer cannot possibly be E (2, 0) as this point lies on the line y=42x (substitute the values of x and y to see that it's true).
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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25 Feb 2012, 07:34
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Hello,
This is how I solved the problem. Since the Slope of line is 2, the line perpendicular to it would have SLope as 1/2. So I used R(4,1) and each options to see which one gives Slope as 1/2. Only option D gives me the co ordinates through which the SLope is 1/2. It took me around a minutes time to solve.
Please let me know if I'm correct ?



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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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25 Feb 2012, 09:30
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priyalr wrote: Hello,
This is how I solved the problem. Since the Slope of line is 2, the line perpendicular to it would have SLope as 1/2. So I used R(4,1) and each options to see which one gives Slope as 1/2. Only option D gives me the co ordinates through which the SLope is 1/2. It took me around a minutes time to solve.
Please let me know if I'm correct ? That's perfectly valid approach. Two lines are perpendicular if and only the product of their slopes is 1. The slope of given line is 2, hence the slope of PR must be 1/2 (negative reciprocal of 2): 1/2*(2)=1. Now, the slope of a line (a line segment) passing through two points \((x_1,y_1)\) and \((x_2,y_2)\) is \(m=\frac{y_2y_1}{x_2x_1}\). So, for our case the slope of PR must be \(m=\frac{1}{2}=\frac{1y_1}{4x_1}\) and you can substitute x and y coordinates of each point from answer choices to see for which one this equation will hold true. Only coordinates of a point from option D fits.
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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01 Jul 2012, 03:10
Bunuel wrote: priyalr wrote: Hello,
This is how I solved the problem. Since the Slope of line is 2, the line perpendicular to it would have SLope as 1/2. So I used R(4,1) and each options to see which one gives Slope as 1/2. Only option D gives me the co ordinates through which the SLope is 1/2. It took me around a minutes time to solve.
Please let me know if I'm correct ? That's perfectly valid approach. Two lines are perpendicular if and only the product of their slopes is 1. The slope of given line is 2, hence the slope of PR must be 1/2 (negative reciprocal of 2): 1/2*(2)=1. Now, the slope of a line (a line segment) passing through two points \((x_1,y_1)\) and \((x_2,y_2)\) is \(m=\frac{y_2y_1}{x_2x_1}\). So, for our case the slope of PR must be \(m=\frac{1}{2}=\frac{1y_1}{4x_1}\) and you can substitute x and y coordinates of each point from answer choices to see for which one this equation will hold true. Only coordinates of a point from option D fits. let's have a look Required slope for line PR = m= 1/2 ( using if two lines are perpendicular then their slopes m1 * m2 = 1 ) option D= ( 0,1) Option E = ( 2, 0) so taking (4,1) and ( 0,1) and finding slope = 2/4 = 1/2 which is of course what we are expecting , now taking (4,1) and (2,0) and finding slope = 1/2 = 1/2 So also E, satisfies the slope method So what am I missing , it is said that only one option satisfies the equation 1/2 = (1y1)/( 4x1) Taking E( 2,0) (10)/(42) = 1/2 and taking D(0,1) (1+1)/(40)= 2/4= 1/2 so both D and E satisfy the slope condition , am I missing anything ?
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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01 Jul 2012, 03:37
stne wrote: Bunuel wrote: priyalr wrote: Hello,
This is how I solved the problem. Since the Slope of line is 2, the line perpendicular to it would have SLope as 1/2. So I used R(4,1) and each options to see which one gives Slope as 1/2. Only option D gives me the co ordinates through which the SLope is 1/2. It took me around a minutes time to solve.
Please let me know if I'm correct ? That's perfectly valid approach. Two lines are perpendicular if and only the product of their slopes is 1. The slope of given line is 2, hence the slope of PR must be 1/2 (negative reciprocal of 2): 1/2*(2)=1. Now, the slope of a line (a line segment) passing through two points \((x_1,y_1)\) and \((x_2,y_2)\) is \(m=\frac{y_2y_1}{x_2x_1}\). So, for our case the slope of PR must be \(m=\frac{1}{2}=\frac{1y_1}{4x_1}\) and you can substitute x and y coordinates of each point from answer choices to see for which one this equation will hold true. Only coordinates of a point from option D fits. let's have a look Required slope for line PR = m= 1/2 ( using if two lines are perpendicular then their slopes m1 * m2 = 1 ) option D= ( 0,1) Option E = ( 2, 0) so taking (4,1) and ( 0,1) and finding slope = 2/4 = 1/2 which is of course what we are expecting , now taking (4,1) and (2,0) and finding slope = 1/2 = 1/2 So also E, satisfies the slope method So what am I missing , it is said that only one option satisfies the equation 1/2 = (1y1)/( 4x1) Taking E( 2,0) (10)/(42) = 1/2 and taking D(0,1) (1+1)/(40)= 2/4= 1/2 so both D and E satisfy the slope condition , am I missing anything ? You can rule out (2,0) (option E), since this point is on the line y=42x.
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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02 Oct 2012, 08:19
ok but why on earth does E also result in slope oh 1/2 ?
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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02 Oct 2012, 08:40



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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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26 Oct 2012, 06:29
Bunuel Bro, my question still remains : I understand E is on the line but why does E also result in slope of 1/2 . . E should cause the slope to be 2 since it is on the line. . why does it then cause the slope to be 1/2? just trying to understand the math of slope here.
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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26 Oct 2012, 06:41



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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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26 Oct 2012, 09:52
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Concrete way is to find the actual coordinates. Slope of RP = 1/2 and by using 4,1 and slope the equation is y=x/2 1 solve for point of intersection  x,y = 2,0. now let P has coordinates (x,y) since intersection is mid point. (x+4)/2 = 2 and (y+1)/2 = 0 thus D
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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02 Nov 2012, 00:45
Quote: solve for point of intersection  x,y = 2,0. How do you get to know the point of intersection is 2,0? I understood your solution till the previous step in which you found the equation of the line.
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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02 Nov 2012, 02:07



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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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11 Nov 2012, 08:08
Bunuel, do you think these coordinates are not unique. Any combination (x,y) for point P that satisfies the equation 22*y = 4x will make RP perpendicular to the line y = 42x. Am I correct to assert that? Brother Karamazov



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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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12 Nov 2012, 10:02



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The line represented by the equation y = 4 – 2x is the [#permalink]
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13 Nov 2012, 03:12
I will go for D slope of MP (with P(a, b)) should be 1/2 thus 1b/4a = 1/2 22*b = 4a only D satisfies this equation But Bunuel, if there were no answers choices, how one could find these values for a and b?



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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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13 Nov 2012, 03:22



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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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09 Sep 2013, 21:18
Hi Bunuel, You drew a descending slope in forward direction that is confusing me, slope should be descending is understandable because m = 2 but why it is in forward direction now backward , i mean why is it not passing through quadrant 3.??
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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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10 Sep 2013, 01:33



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Re: The line represented by the equation y = 4 – 2x is the [#permalink]
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12 Sep 2013, 17:52
Hello Bunuel, Request you to please validate my approach: We know that perpendicular bisector bisects the line into two equal halves. Since, line given is the perpendicular bisector of line segment RP. hence, point M will be the midpoint of line segment RP,. Using mid point formula Let point of P(x,y) So, (x+4)/2=2 (y+1)/2 = 0 Hence, coordinates are (0,1). Is this a valid approach or answer just happens to be correct/.
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