Precalculus Examples

$(- 3, - 4)$ , $(- 2, - 9)$

Step 1

Find the value of the slope.

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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.

$m = \frac{- 9 - (- 4)}{- 2 - (- 3)}$

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 $- 4$ .

$m = \frac{- 9 + 4}{- 2 - (- 3)}$

Step 1.4.1.2

Add $- 9$ and $4$ .

$m = \frac{- 5}{- 2 - (- 3)}$

Step 1.4.2

Simplify the denominator.

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Step 1.4.2.1

Multiply $- 1$ by $- 3$ .

$m = \frac{- 5}{- 2 + 3}$

Step 1.4.2.2

Add $- 2$ and $3$ .

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

Step 1.4.3

Divide $- 5$ by $1$ .

$m = - 5$

Step 2

Find the value of the y-intercept.

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Step 2.1

Substitute the value of $m$ into the slope-intercept form of the equation, $y = m x + b$ .

$y = (- 5) \cdot x + b$

Step 2.2

Substitute the value of $x$ into the slope-intercept form of the equation, $y = m x + b$ .

$y = (- 5) \cdot (- 3) + b$

Step 2.3

Substitute the value of $y$ into the slope-intercept form of the equation, $y = m x + b$ .

$- 4 = (- 5) \cdot (- 3) + b$

Step 2.4

Rewrite the equation as $(- 5) \cdot (- 3) + b = - 4$ .

$(- 5) \cdot (- 3) + b = - 4$

Step 2.5

Multiply $- 5$ by $- 3$ .

$15 + b = - 4$

Step 2.6

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

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Step 2.6.1

Subtract $15$ from both sides of the equation.

$b = - 4 - 15$

Step 2.6.2

Subtract $15$ from $- 4$ .

$b = - 19$

Step 3

List the slope and y-intercept.

Slope: $- 5$

y-intercept: $(0, - 19)$

Step 4

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