Precalculus Examples

$(1, 13)$ , $(0, 9)$

Step 1

Find the slope of the line between $(1, 13)$ and $(0, 9)$ using $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ , which is the change of $y$ over the change of $x$ .

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Step 1.1

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

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

Step 1.2

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).

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

Step 1.3

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

$m = \frac{9 - (13)}{0 - (1)}$

Step 1.4

Simplify.

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Step 1.4.1

Simplify the numerator.

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Step 1.4.1.1

Multiply $- 1$ by $13$ .

$m = \frac{9 - 13}{0 - (1)}$

Step 1.4.1.2

Subtract $13$ from $9$ .

$m = \frac{- 4}{0 - (1)}$

Step 1.4.2

Simplify the denominator.

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Step 1.4.2.1

Multiply $- 1$ by $1$ .

$m = \frac{- 4}{0 - 1}$

Step 1.4.2.2

Subtract $1$ from $0$ .

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

Step 1.4.3

Divide $- 4$ by $- 1$ .

$m = 4$

Step 2

Use the slope $4$ and a given point $(1, 13)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (13) = 4 \cdot (x - (1))$

Step 3

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

$y - 13 = 4 \cdot (x - 1)$

Step 4

Solve for $y$ .

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Step 4.1

Simplify $4 \cdot (x - 1)$ .

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Step 4.1.1

Rewrite.

$y - 13 = 0 + 0 + 4 \cdot (x - 1)$

Step 4.1.2

Simplify by adding zeros.

$y - 13 = 4 \cdot (x - 1)$

Step 4.1.3

Apply the distributive property.

$y - 13 = 4 x + 4 \cdot - 1$

Step 4.1.4

Multiply $4$ by $- 1$ .

$y - 13 = 4 x - 4$

Step 4.2

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

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Step 4.2.1

Add $13$ to both sides of the equation.

$y = 4 x - 4 + 13$

Step 4.2.2

Add $- 4$ and $13$ .

$y = 4 x + 9$

Step 5

List the equation in different forms.

Slope-intercept form:

$y = 4 x + 9$

Point-slope form:

$y - 13 = 4 \cdot (x - 1)$

Step 6

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