Equation for the line that passes through... points.

DOES anyone know how to do this problem?


Write an equation for the line that passes through the points (-5, 5) and (-3,9).

A. y= 2x +5 B. y= -2x +3

C. y= 3x +20 D. y= 2x +15

i know the answer is D. but what are the steps to D? Help please! :/

You should have various "Forms" at your disposal.

Do you have the Two-Point Form or the Point-Slope Form? You will need one of them.

Can you calculate the Slope of the line, based on the location of those two points?

Well, you are given all the information you need to solve this - if you know the point-slope formula (which tkhunny mentioned). The point-slope formula is:

y - y1 = m (x - x1)

where (y1,x1) are coordinates that you already know, and m is the slope that in this case you are solving for using your two given points, (-5, 5) and (-3,9). So first, plug your given points into the equation. Either set of coordinates can be plugged in for (y,x) or (y1,x1) - you should get the same answer.

9 - 5 = m ((-3) - (-5))
4 = m (2)
2 = m

Now plug in one set of coordinates for (y1,x1) and m (which you have just solved for) back into the point-slope formula:

y - 9 = (2) (x - (-3))
y - 9 = (2) (x + 3)
y - 9 = 2x + 6
y = 2x + 6 + 9


y = 2x + 15


which is answer choice D! Hope you get it, or understand a little better how that answer is arrived at.