Find the equation of the line through the points (–1, –5) and (4, 5). First, find the slope: m = rise / run = 5/10 = 1/2.
Then the equation is y-5=(1/2)(x-4). If (a,1) is on this line, (a,1) must satisfy the given equation. Let y=1 and solve for x:
1-5 = (1/2)(x-4) Mult both sides by 2 to get -2 = x-4. Then x = -4+2 = -2
So (-2,1) is also on the line.
