Coordinate Geometry

[sukhman]

Find the equation of a straight line perpendicular to straight line 3x+4y=7 and passing through the point (3, -3)

[theCodeToGMAT]

Find the equation of a straight line perpendicular to straight line 3x+4y=7 and passing through the point (3, -3)

Can you post the Answer choices as well.

[sukhman]

well the answer is [spoiler]4x-3y=21[/spoiler]

[theCodeToGMAT]

3x + 4y = 7
Slope = -3/4

For Perpendicular lines, product of slopes of two lines must be "-1"

(-3/4) x m = -1
m = 4/3

Now, the line passes by (3,-3) & has slope (4/3)
y = mx + c
-3 = (4/3)(3) + c
c = -7

So, equation:
y = (4/3)x - 7

3y = 4x - 21

[[email protected]]

Hi sikhman,

The GMAT Quant section is NOT a typical "math test" because you will have 5 answers to choose from and sometimes an important "hint" or pattern about the question can be deduced from the 5 choices. If you don't pay attention to the 5 answers (or in this case, don't post them), then you will likely force yourself into using a "math" approach, which might not be the most efficient/easiest way to solve the problem.

As an example, in this this question, we know that we need a line that is:
1) Perpendicular to 3x + 4y = 7
2) Passes through the point (3, -3)

That second fact is interesting in that we COULD plug in x = 3, y = -3 into the five options. If THAT solution doesn't fit any of those 5 answers, then those answers can be eliminated. Most GMAT Quant questions are designed with multiple approaches in mind; it's a way to test how flexible a thinker you are. So, in the future, you should post the 5 answers and consider what they offer you (in terms of options and information) - you might just discover a faster alternative to doing math.

GMAT assassins aren't born, they're made,
Rich