Two points determine a line. In slope intercept form we have:
y = -2x + b
So:
-12 = -2(3) + b and [first equation]
k = -2(6) + b [second equation]
We have a system of simultaneous equations with two unknowns. The first is trivially easy to solve:
-12 = -6 + b [Evaluate -2(3)]
-6 = b [Add +6 to each side]
So we substitute this into the second equation:
k = -2(6) + -6 = -18
We could double check our work knowing that m=Δy/Δx
We expect m to be -2. Does:
-2 = (-18 - -12)/(6 - 3) = -6/3 = -2?
;)
