"Points R,S, and T are Collinear. Find y..."?

Question

Hi guys,

Here's the question:

Points R (0,0), S (-4,y) and T (6,-3) are collinear. Find y.

I didn't know how to solve this question, so I just graphed the points. I found the answer to be y=2.

I got the answer right, but she told me to show my work.

How do I solve a question like this?!?!


Thank you guys SO MUCH.

Answer 1

You know from looking at points R and T that the slop of the line is -2. You can use this to find T:

slope = (y2 - y1) / (x2 - x1)

-1/2 = (-3 - y) / (6 + 4)

-1/2 = (-3 - y) / (10)

-5 = -3 - y

y = 2

Answer 2

Find the equation of the line with R and T first put in y = mx + b form. Then substitute in pt S and solve/simplify to get y.