Find the Equation Using Point-Slope Formula (-1,-4) , (-5,-5)

$(- 1, - 4)$ , $(- 5, - 5)$

Step 1

Find the slope of the line between $(- 1, - 4)$ and $(- 5, - 5)$ 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.

$m = \frac{- 5 - (- 4)}{- 5 - (- 1)}$

Simplify.

Simplify the numerator.

Multiply $- 1$ by $- 4$ .

$m = \frac{- 5 + 4}{- 5 - (- 1)}$

Add $- 5$ and $4$ .

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

Simplify the denominator.

Multiply $- 1$ by $- 1$ .

$m = \frac{- 1}{- 5 + 1}$

Add $- 5$ and $1$ .

$m = \frac{- 1}{- 4}$

Dividing two negative values results in a positive value.

$m = \frac{1}{4}$

Step 2

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

$y - (- 4) = \frac{1}{4} \cdot (x - (- 1))$

Step 3

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

$y + 4 = \frac{1}{4} \cdot (x + 1)$

Step 4

Solve for $y$ .

Simplify $\frac{1}{4} \cdot (x + 1)$ .

Rewrite.

$y + 4 = 0 + 0 + \frac{1}{4} \cdot (x + 1)$

Simplify by adding zeros.

$y + 4 = \frac{1}{4} \cdot (x + 1)$

Apply the distributive property.

$y + 4 = \frac{1}{4} x + \frac{1}{4} \cdot 1$

Combine $\frac{1}{4}$ and $x$ .

$y + 4 = \frac{x}{4} + \frac{1}{4} \cdot 1$

Multiply $\frac{1}{4}$ by $1$ .

$y + 4 = \frac{x}{4} + \frac{1}{4}$

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

Subtract $4$ from both sides of the equation.

$y = \frac{x}{4} + \frac{1}{4} - 4$

To write $- 4$ as a fraction with a common denominator, multiply by $\frac{4}{4}$ .

$y = \frac{x}{4} + \frac{1}{4} - 4 \cdot \frac{4}{4}$

Combine $- 4$ and $\frac{4}{4}$ .

$y = \frac{x}{4} + \frac{1}{4} + \frac{- 4 \cdot 4}{4}$

Combine the numerators over the common denominator.

$y = \frac{x}{4} + \frac{1 - 4 \cdot 4}{4}$

Simplify the numerator.

Multiply $- 4$ by $4$ .

$y = \frac{x}{4} + \frac{1 - 16}{4}$

Subtract $16$ from $1$ .

$y = \frac{x}{4} + \frac{- 15}{4}$

Move the negative in front of the fraction.

$y = \frac{x}{4} - \frac{15}{4}$

Step 5

Reorder terms.

$y = \frac{1}{4} x - \frac{15}{4}$

Step 6

List the equation in different forms.

Slope-intercept form:

$y = \frac{1}{4} x - \frac{15}{4}$

Point-slope form:

$y + 4 = \frac{1}{4} \cdot (x + 1)$

Step 7

Find the Equation Using Point-Slope Formula (-1,-4) , (-5,-5)

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