Question

Find the equation of the line that passes through the points (-2, 1) and (1, -2).

Answer 1

We'll build slope-intercept equation because you can easily see the slope and y-intercept.

To find the slope with two points:
`m = (y_2 - y_1)/(x_2 - x_1)`


`(-2 - 1)/(1 - (-2)) = (-3)/(3) = -1`

Great, we have the slope, but we need y-intercept to complete the slope-intercept equation.

We already have the partially constructed slope-intercept equation: y = -1x + b

If substitute the x and y variables for an ordered pair, we can solve for b.

I use the ordered pair (1, -2)

-2 = -1(1) + b
-2 = -1 + b
-1 = b <-- Add 1 to each side

So, the slope-intercept equation is y = -1m - 1

Answer 2

slope = (-2-1)/(1+2) = -1

y = mx + b
1 = -1(-2) + b
b = -1

equation
y = -x - 1