Find the Equation Using Point-Slope Formula (3,-15) , (-4,13)

$(3, - 15)$ , $(- 4, 13)$

Step 1

Find the slope of the line between $(3, - 15)$ and $(- 4, 13)$ 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.

$m = \frac{13 - (- 15)}{- 4 - (3)}$

Simplify.

Simplify the numerator.

Multiply $- 1$ by $- 15$ .

$m = \frac{13 + 15}{- 4 - (3)}$

Add $13$ and $15$ .

$m = \frac{28}{- 4 - (3)}$

Simplify the denominator.

Multiply $- 1$ by $3$ .

$m = \frac{28}{- 4 - 3}$

Subtract $3$ from $- 4$ .

$m = \frac{28}{- 7}$

Divide $28$ by $- 7$ .

$m = - 4$

Step 2

Use the slope $- 4$ and a given point $(3, - 15)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (- 15) = - 4 \cdot (x - (3))$

Step 3

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

$y + 15 = - 4 \cdot (x - 3)$

Step 4

Solve for $y$ .

Simplify $- 4 \cdot (x - 3)$ .

Rewrite.

$y + 15 = 0 + 0 - 4 \cdot (x - 3)$

Simplify by adding zeros.

$y + 15 = - 4 \cdot (x - 3)$

Apply the distributive property.

$y + 15 = - 4 x - 4 \cdot - 3$

Multiply $- 4$ by $- 3$ .

$y + 15 = - 4 x + 12$

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

Subtract $15$ from both sides of the equation.

$y = - 4 x + 12 - 15$

Subtract $15$ from $12$ .

$y = - 4 x - 3$

Step 5

List the equation in different forms.

Slope-intercept form:

$y = - 4 x - 3$

Point-slope form:

$y + 15 = - 4 \cdot (x - 3)$

Step 6

Find the Equation Using Point-Slope Formula (3,-15) , (-4,13)

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