Find the Equation Using Point-Slope Formula (2,1) , (5,-8)

$(2, 1)$ , $(5, - 8)$

Step 1

Find the slope of the line between $(2, 1)$ and $(5, - 8)$ using $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ , which is the change of $y$ over the change of $x$ .

Slope is equal to the change in $y$ over the change in $x$ , or rise over run.

$m = \frac{change in y}{change in x}$

The change in $x$ is equal to the difference in x-coordinates (also called run), and the change in $y$ is equal to the difference in y-coordinates (also called rise).

$m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$

Substitute in the values of $x$ and $y$ into the equation to find the slope.

$m = \frac{- 8 - (1)}{5 - (2)}$

Simplify.

Simplify the numerator.

Multiply $- 1$ by $1$ .

$m = \frac{- 8 - 1}{5 - (2)}$

Subtract $1$ from $- 8$ .

$m = \frac{- 9}{5 - (2)}$

Simplify the denominator.

Multiply $- 1$ by $2$ .

$m = \frac{- 9}{5 - 2}$

Subtract $2$ from $5$ .

$m = \frac{- 9}{3}$

Divide $- 9$ by $3$ .

$m = - 3$

Step 2

Use the slope $- 3$ and a given point $(2, 1)$ to substitute for $x_{1}$ and $y_{1}$ in the point-slope form $y - y_{1} = m (x - x_{1})$ , which is derived from the slope equation $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (1) = - 3 \cdot (x - (2))$

Step 3

Simplify the equation and keep it in point-slope form.

$y - 1 = - 3 \cdot (x - 2)$

Step 4

Solve for $y$ .

Simplify $- 3 \cdot (x - 2)$ .

Rewrite.

$y - 1 = 0 + 0 - 3 \cdot (x - 2)$

Simplify by adding zeros.

$y - 1 = - 3 \cdot (x - 2)$

Apply the distributive property.

$y - 1 = - 3 x - 3 \cdot - 2$

Multiply $- 3$ by $- 2$ .

$y - 1 = - 3 x + 6$

Move all terms not containing $y$ to the right side of the equation.

Add $1$ to both sides of the equation.

$y = - 3 x + 6 + 1$

Add $6$ and $1$ .

$y = - 3 x + 7$

Step 5

List the equation in different forms.

Slope-intercept form:

$y = - 3 x + 7$

Point-slope form:

$y - 1 = - 3 \cdot (x - 2)$

Step 6

Find the Equation Using Point-Slope Formula (2,1) , (5,-8)

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