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Co-ordinates

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Co-ordinates

by Claret » Fri Jun 19, 2009 4:52 am
In xy plane, does the line y = 3x + 2 contain point (r, s)? C
a. (3r + 2 –s)(4r + 9 – s) = 0
b. (4r – 6 – s)(3r + 2 – s) = 0
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by mike22629 » Fri Jun 19, 2009 5:31 am
3r + 2 - s MUST equal 0 because it is in both equations.

The reason for this is that the other two equations are both different, hence both of them can not equal 0.

3r + 2 = s

same as

3x + 2 = y

IMO C
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I might be missing something

by disco82 » Fri Jun 19, 2009 6:13 am
But why can't it be D? Since 3r-s=-2 emerges as a root for both equations?
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by Claret » Fri Jun 19, 2009 6:18 am
it is not D because

if A * B = 0
then there are 3 possibilities
1-only A= 0
2 - only B =0
3 - both A and B = 0

therefore

if (3r + 2 –s)(4r + 9 – s) = 0

we cannot surely say that (3r+2-s) = 0

hope it helps !
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