Question

What is the equation of the line that contains the two points (0,-1) and (-1,-3)?

Answer 1

Remark

Right away when the x value of one of the points = 0 then you have the y intercept.

-1 = 0*m + b

b = - 1

So far what you have is y = mx - 1. Now use the two points to get the slope (m)

x1 = 0

x2 = -1

y1 = -1

y2 = - 3

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

m = (-3 - - 1) / (-1 - 0)

m = -2/-1 = 2

The answer to the equation is

y = 2x - 1

Note

The best way to check this is with a graph. The two given points are marked on the graph. The upper one is (0 , -1). The lower one is (-1 , -3). The slope must be correct.

Answer 2

The answer is in this picture