Question

So im doing slope intercept from two points, what is the equation of the line through (2,1) and (5,-8). what does y equal?

Answer 1

Use rise over run to determine the slope of the equation.

Rise over run uses the following formula:

y2 - y1 / x2 - x1

Plug in your points' values into this formula.


`(-8 - 1)/(5-2) = (-9)/(3) = -3`

Use the slope to find the y-intercept of the equation. Take a point on the line, and apply the slope to it to find the y-intercept.

Take the point (2,1) and subtract the x-value so that it equals 0.


`2 - 2 = 0`

Since we moved the point back by 2, we'll multiply our slope by -2, and add the result to the y-value to find our new point.


`(-2 * -3) + 1 = 6 + 1 = 7`

Our new point is now (0,7). Since x = 0, the y-value will be our y-intercept. The y-intercept is 7.

Slope-intercept form uses the following formula:


`y = mx + b`

m is your slope, and b is your y-intercept. We have already found those values, so plug them into the formula.

The following equation is your answer:


`y = -3x + 1`