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Mon 19 Jul, 2004 06:44 am
How do you find an equation in standard form of a line point P that is perpendicular to line L, where:
P: (-1,2)
L: x-3y=-2
It's been a long time since I've done this, so PLEASE check this out in your textbook. As close as I can remember, and figure out, perpendicular lines have negative reciprocal slopes.
The first thing to do is to put the equation of your line into standard form. x-3y = -2 then becomes:
y = x/3 + 2/3
so the slope of your first line is 1/3.
Iff (not a typo - it stands for "if and only if") my memory is correct, then to be perpendicular, the second line must have a slope of -3 to be a negative reciprocal.
Your second line is now in the form of:
y= -3x + b.
To solve for b, plug in the point (-1,2) from the problem statement:
2 = (-3)(-1) +b
2= 3+b
-1 = b
so the answer is y = -3x-1
I just graphed up the two lines, and they do look perpendicular.