Find the Equation Using Point-Slope Formula (4,12) , (5,15)

$(4, 12)$ , $(5, 15)$

Step 1

Find the slope of the line between $(4, 12)$ and $(5, 15)$ 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.

$m = \frac{15 - (12)}{5 - (4)}$

Simplify.

Simplify the numerator.

Multiply $- 1$ by $12$ .

$m = \frac{15 - 12}{5 - (4)}$

Subtract $12$ from $15$ .

$m = \frac{3}{5 - (4)}$

Simplify the denominator.

Multiply $- 1$ by $4$ .

$m = \frac{3}{5 - 4}$

Subtract $4$ from $5$ .

$m = \frac{3}{1}$

Divide $3$ by $1$ .

$m = 3$

Step 2

Use the slope $3$ and a given point $(4, 12)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (12) = 3 \cdot (x - (4))$

Step 3

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

$y - 12 = 3 \cdot (x - 4)$

Step 4

Solve for $y$ .

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

Rewrite.

$y - 12 = 0 + 0 + 3 \cdot (x - 4)$

Simplify by adding zeros.

$y - 12 = 3 \cdot (x - 4)$

Apply the distributive property.

$y - 12 = 3 x + 3 \cdot - 4$

Multiply $3$ by $- 4$ .

$y - 12 = 3 x - 12$

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

Add $12$ to both sides of the equation.

$y = 3 x - 12 + 12$

Combine the opposite terms in $3 x - 12 + 12$ .

Add $- 12$ and $12$ .

$y = 3 x + 0$

Add $3 x$ and $0$ .

$y = 3 x$

Step 5

List the equation in different forms.

Slope-intercept form:

$y = 3 x$

Point-slope form:

$y - 12 = 3 \cdot (x - 4)$

Step 6

Find the Equation Using Point-Slope Formula (4,12) , (5,15)

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