We'll use y = mx + b
First, we need to find the slope, (m)........this is defined as ......the change in y / change in x
Look at (4, 5) and (-8, -4)
Note that, from the first point to the second, y changes by -9
And x changes by -12
So.....the slope is -9 / -12 = -3 / -4 = 3/4 = "m"
Now using either one of the points - i'll use the first one -we can substitute for y, m and x in y = mx + b to find "b"....so we have
5= (3/4)(4) + b simplify
5= 3 + b subtract 3 from both sides
b = 2
So our equation is
y = (3/4)x + 2
Check to see that the second point "works" in this equation.....just fill in for "x" and "y'
Does that help??
