the slope of a line is -4 and its y-intercept is (0,4). what is the equation of the line that's perpendicular to the first line and passes through (-8,2).

Question

e.mccormick · Answer

Do you know the relationship between the slopes of perpendicular lines?

e.mccormick · Answer

If you do, then solve for the perpendicular slopw, then use point-slope form to solve this.

anonymous · Answer

nope. thats all the question says... our math teacher isnt that grea

e.mccormick · Answer

You should have learned the slope relationship before this point, but may not remember it.  Let me do an example.

anonymous · Answer

great* and im guessing thats where i get lost casue i know the y=mx+b and the y-y1=m(x-x1) but dont know when to use them...

e.mccormick · Answer

Pkay, here are line 1 and 2, and they are perpendicular.
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e.mccormick · Answer

The slope of Line 1 is the change in y over the change in x for line 1.  This is also called "Rise over Run" or "Delta Y over Delta X"

In this case, the rise is 2 and the run is 3, so te slope is 2/3.

e.mccormick · Answer

With me to that point?

anonymous · Answer

yup

e.mccormick · Answer

If you look at the second line, the "rise" is not a rise at all!  It is a drop of 3.  For a rise to drop, it is negative.  So the rise over run is -3/2.

So if we look at those slopes side by side we have:
$$\frac{2}{3}\, \,\mathrm{and}\;-\frac{3}{2}$$
Do you see the realtionship there?

e.mccormick · Answer

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