Help explain this Alg. Problem

Please don't tell me the answer, because I already know it. I just need to know how to get to the answer, and I've tried a couple times, but I just can't seem to get it. My answer ends up being something like (y = -1.5x + 19/12), but the answer is (y = -0.5x + 1.5).

You're supposed to find the slope-intercept form of a the equation of the line that passes through points (2, 0.5) (0.5, 1.25)

I'm not sure if it's from the lack of practice over the summer or the lack of actually trying to learn this last year, but it's probably both.

Thanks for helping

OK

Slope intercept form: y = mx+b

First find the slope (m)

(y2 - y1) / (x2 - x1)

1.25 - .5 / .5 - 2
= .75/1.5
= -.5

So now we know the slope = -.5
So
y = -.5x + b ; to find b, place one of the points in here

.5 = -.5(2) + b
.5 = -1 + b
1.5 = b

So now we have the intercept

y = -.5x + 1.5

Prove it with the second point

1.25 = -.5(.5) + 1.5 ??
1.25 = -.25 + 1.5 ??
1.25 = 1.25 YES!!

Hope that helps.

1. plug in the numbers in y=ax+b,
then you'll get these:

0.5 = 2a +b
1.25 = 0.5a+b

2. for the sake of convenience, multiply 4 on the second equation and get
5 = 2a +4b

then subtract the first equation from the second

5 = 2a + 4b
-)0.5 = 2a+b
-------------------------
4.5 = 3b
b=1.5
a=-0.5

Hope this helped :)

It's ok, sometimes with math, you forget how to do stuff.

So first thing's first, the reason why you are given two points to find the equation of the line (not three, not four), is that you can only make one specific line given any two points.

The formula to solve this problem is given here:

(y - y1) / (x-x1) = (y2 - y1) / (x2 - x1) where (x1, y1) and (x2, y2) are the coordinate points given to you