What's the equation of the secant line containing (1, f(1)) and (2, f(2))

f(x) = 1 - 3x

Explain please!

Use the standard formula for slope: change in y divided the change in x. Get the y-values:

f(1) = 1 - 3(1) = -2, and f(2) = 1 - 3(2) = -5.

The two points are therefore (1, -2) and (2, -5). The slope is

m = (-5 - (-2))/(2 - 1) = -3/1 = -3.