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line m (not shown)

by sanju09 » Wed Jul 07, 2010 4:52 am
In the x y-coordinate plane attached, line l contains the points (0, 0) and (1, 2). If line m (not shown) contains the point (0, 0) and is perpendicular to l, what is an equation of m?
(A) y = - ½ x
(B) y = - ½ x + 1
(C) y = - x
(D) y = - x + 2
(E) y = - 2 x
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by gmatmachoman » Wed Jul 07, 2010 4:54 am
Pick A

Line L

y = 2x

Line m is perpendicular to L


product of slopes = -1


M2 = -1/2

So the line m will be of y = -1/2 X +C

To get C, apply thge values of (x,y) : (0,0)
C = 0
So y = -1/2 X

Pick A
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by diebeatsthegmat » Sun Jul 18, 2010 12:03 pm
sanju09 wrote:In the x y-coordinate plane attached, line l contains the points (0, 0) and (1, 2). If line m (not shown) contains the point (0, 0) and is perpendicular to l, what is an equation of m?
(A) y = - ½ x
(B) y = - ½ x + 1
(C) y = - x
(D) y = - x + 2
(E) y = - 2 x
nah nah nah, the answer should be E
we can fine the slop of m by writing equation of l
since l contains the point (o,o) and (1,2) we have (y-0)/(x-0)=(1-0)/(2-0)
and we easily find l : y=1/2x
because slop (a) of m and l are perpendicular so
a.1/2=-1 or a =-2
so m must be E
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by kvcpk » Sun Jul 18, 2010 12:10 pm
diebeatsthegmat wrote:
nah nah nah, the answer should be E
we can fine the slop of m by writing equation of l
since l contains the point (o,o) and (1,2) we have (y-0)/(x-0)=(1-0)/(2-0)
and we easily find l : y=1/2x
because slop (a) of m and l are perpendicular so
a.1/2=-1 or a =-2
so m must be E
You made a mistake in calculating the line equation.
(y-0)/(x-0)=(1-0)/(2-0) is wrong
(y-0)/(x-0)=(2-0)/(1-0) is right.
So equation is y=2x.
Hence the line perpendicular will have slope -1/2
pick A.

One more thing. You need not calculate the line equation. Just calculate the slope and see which answer suits..

Hope this helps!!
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by debmalya_dutta » Sun Jul 18, 2010 1:58 pm
Yep..I am with A too
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