Find the Equation Using Point-Slope Formula (-1.5,-12.5) , (0,-8)

$(- 1.5, - 12.5)$ , $(0, - 8)$

Step 1

Find the slope of the line between $(- 1.5, - 12.5)$ and $(0, - 8)$ 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.

$m = \frac{- 8 - (- 12.5)}{0 - (- 1.5)}$

Simplify.

Simplify the numerator.

Multiply $- 1$ by $- 12.5$ .

$m = \frac{- 8 + 12.5}{0 - (- 1.5)}$

Add $- 8$ and $12.5$ .

$m = \frac{4.5}{0 - (- 1.5)}$

Simplify the denominator.

Multiply $- 1$ by $- 1.5$ .

$m = \frac{4.5}{0 + 1.5}$

Add $0$ and $1.5$ .

$m = \frac{4.5}{1.5}$

Divide $4.5$ by $1.5$ .

$m = 3$

Step 2

Use the slope $3$ and a given point $(- 1.5, - 12.5)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (- 12.5) = 3 \cdot (x - (- 1.5))$

Step 3

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

$y + 12.5 = 3 \cdot (x + 1.5)$

Step 4

Solve for $y$ .

Simplify $3 \cdot (x + 1.5)$ .

Rewrite.

$y + 12.5 = 0 + 0 + 3 \cdot (x + 1.5)$

Simplify by adding zeros.

$y + 12.5 = 3 \cdot (x + 1.5)$

Apply the distributive property.

$y + 12.5 = 3 x + 3 \cdot 1.5$

Multiply $3$ by $1.5$ .

$y + 12.5 = 3 x + 4.5$

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

Subtract $12.5$ from both sides of the equation.

$y = 3 x + 4.5 - 12.5$

Subtract $12.5$ from $4.5$ .

$y = 3 x - 8$

Step 5

List the equation in different forms.

Slope-intercept form:

$y = 3 x - 8$

Point-slope form:

$y + 12.5 = 3 \cdot (x + 1.5)$

Step 6

Find the Equation Using Point-Slope Formula (-1.5,-12.5) , (0,-8)

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