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In the XY plane, does the line with equation y=3x+2

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Re: In the XY plane, does the line with equation y=3x+2 [#permalink]

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New post 30 Aug 2013, 14:41
Bunuel,

In statement (1), you have said that we have these possibilities:
(3r + 2 - s) = 0 OR (4r + 9 - s) = 0 OR both.

But, when we have something like this:
(x + 3)(x+5) = 0

In this case, there are only two possibilities, right? (x+3)=0 OR (x+5)=0.
Both cannot be zero at the same time because "x" represents a single and unique value.
Please confirm.
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Re: In the XY plane, does the line with equation y=3x+2 [#permalink]

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New post 31 Aug 2013, 05:13
danzig wrote:
Bunuel,

In statement (1), you have said that we have these possibilities:
(3r + 2 - s) = 0 OR (4r + 9 - s) = 0 OR both.

But, when we have something like this:
(x + 3)(x+5) = 0

In this case, there are only two possibilities, right? (x+3)=0 OR (x+5)=0.
Both cannot be zero at the same time because "x" represents a single and unique value.
Please confirm.


Yes.

(3r + 2 - s) = 0 and (4r + 9 - s) = 0 can both be true, for r=-7 and s=-19.

But for (x+3)=0 and (x+5)=0 both cannot be true simultaneously. Either x=-3 or x=-5.

Hope it's clear.
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Re: In the XY plane, does the line with equation y=3x+2 [#permalink]

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New post 07 Jun 2014, 11:40
could we also think of it as:

the following two equations define two non-identical hyperbola.
1) (3r+2-s) (4r+9-s)=0
2) (4r-6-s) (3r+2-s)=0

each equation represents a set of points on different hyperbola
since the question states that (r,s) is one point,
it must be a single intersection of the two hyperbola which cannot be found without both equations.

therefore: you need both equations to define one point (r,s) and then you can easily solve for whether (r,s) satisfies the first equation y = 3x+2

would that reasoning also work?
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In the XY plane, does the line with equation y=3x+2 [#permalink]

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New post 25 Nov 2014, 11:28
(Just so I get the whole picture) Say, instead of the bold parts in (3r+2-s)(4r+9-s)=0 and (4r-6-s)(3r+2-s)=0, there are 2 slightly unrelated terms like 5r-3-s and 2r+7-s.They would remain to be possibilities of the equation and E would be the right choice, right?
Sorry if I am complicating things.

Last edited by deeuk on 26 Nov 2014, 10:36, edited 1 time in total.
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Re: In the XY plane, does the line with equation y=3x+2 [#permalink]

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New post 26 Nov 2014, 04:46
deeuk wrote:
(Just so I get the whole picture) Say, instead of the bold parts in (3r+2-s)(4r+9-s)=0 and (4r-6-s)(3r+2-s)=0, there were 2 slightly unrelated terms like 5r-3-s and 2r+7-s, they would remain to be possibilities of the equation and E would be the right choice, right?
Sorry if I am complicating things.


Yes, in this case the answer would be E.
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In the xy plane, does the line y=3x+2 contain the point (r,s)? i) (3r+ [#permalink]

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New post 01 Aug 2015, 22:38
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In the xy plane, does the line y=3x+2 contain the point (r,s)?
i) (3r+2-s)(4r+9-s)=0
ii) (4r-6-s)(3r+2-s)=0
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Re: In the xy plane, does the line y=3x+2 contain the point (r,s)? i) (3r+ [#permalink]

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New post 02 Aug 2015, 02:24
visram04 wrote:
In the xy plane, does the line y=3x+2 contain the point (r,s)?
i) (3r+2-s)(4r+9-s)=0
ii) (4r-6-s)(3r+2-s)=0



Question Stem: If Point (r,s) lies on the line y =3x+2, then the point should satisfy the equation, i.e., s=3r+2

St 1: (3r+2-s)(4r+9-s)=0

3r+2 = s or 4r+9 =s
We dont have unique solution. Hence not sufficient

St 2: (4r-6-s)(3r+2-s)=0


4r-6 = s or 3r+2 = s
We dont have unique solution. Hence not sufficient

Combined:

Combining we get s = 3r+2 --> which is required to prove from the question stem.
Hence sufficient.
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In the XY plane, does the line with equation y=3x+2 [#permalink]

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New post 22 Mar 2016, 03:32
gaurav2k101 wrote:
In the xy-plane , does the line with equation y=3x+2 contains the point(r,s)?

(1) (3r+2-s)(4r+9-s)=0
(2) (4r-6-s)(3r+2-s)=0



I did it differently, but it could be totally wrong. It would be good if someone can check it. Bunuel I would highly appreciate it if you check it.

I substituted 0 for r for both statements,

(1) (3(0)+2-s)(4(0)+9-s)=0 so that s=2 (which is on the line) or 9 (which is not on the line)

(2) (4(0)-6-s)(3(0)+2-s)=0 so that s=6 (which is not on the line) or 2 (which is on the line)

Alone statement 1 and 2 are insufficient since they could be either 1 of 2 values, but together they prove that s=2, so the answer is C.
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Re: In the XY plane, does the line with equation y=3x+2 [#permalink]

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New post 05 Aug 2016, 09:07
Substituting variables r and s for x and y is very smart. Then the question becomes a logic question.

(1) can contain the point or it could not
(2) can contain the point or could not (just like statement 1)

Together at first it looks like it will not work out, however it has to have the point because the other two equations could not satisfy both of the equations. It would be 4r + 9 = 4r - 6 which would never work.
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Re: In the XY plane, does the line with equation y=3x+2 [#permalink]

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New post 20 Aug 2016, 09:25
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Guys, please say if I am wrong.
If the question was found that
1) (3r+3-s) (4r+9-s)=0
2) (4r-6-s) (3r+3-s)=0
then we will conclud that the answer is C, do not contain since parallel

If the question was found that
1) (4r+2-s) (4r+9-s)=0
2) (4r-6-s) (4r+2-s)=0
then we will conclud that the answer is C, contain since intercept

am I right?
Re: In the XY plane, does the line with equation y=3x+2   [#permalink] 20 Aug 2016, 09:25

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