Algebra Examples

$(1, 8)$ and $(- 2, - 1)$

Step 1

Find the slope of the line between $(1, 8)$ and $(- 2, - 1)$ 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.

$m = \frac{- 1 - (8)}{- 2 - (1)}$

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 $8$ .

$m = \frac{- 1 - 8}{- 2 - (1)}$

Step 1.4.1.2

Subtract $8$ from $- 1$ .

$m = \frac{- 9}{- 2 - (1)}$

Step 1.4.2

Simplify the denominator.

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Step 1.4.2.1

Multiply $- 1$ by $1$ .

$m = \frac{- 9}{- 2 - 1}$

Step 1.4.2.2

Subtract $1$ from $- 2$ .

$m = \frac{- 9}{- 3}$

Step 1.4.3

Divide $- 9$ by $- 3$ .

$m = 3$

Step 2

Use the slope $3$ and a given point $(1, 8)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (8) = 3 \cdot (x - (1))$

Step 3

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

$y - 8 = 3 \cdot (x - 1)$

Step 4

Solve for $y$ .

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Step 4.1

Simplify $3 \cdot (x - 1)$ .

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Step 4.1.1

Rewrite.

$y - 8 = 0 + 0 + 3 \cdot (x - 1)$

Step 4.1.2

Simplify by adding zeros.

$y - 8 = 3 \cdot (x - 1)$

Step 4.1.3

Apply the distributive property.

$y - 8 = 3 x + 3 \cdot - 1$

Step 4.1.4

Multiply $3$ by $- 1$ .

$y - 8 = 3 x - 3$

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 $8$ to both sides of the equation.

$y = 3 x - 3 + 8$

Step 4.2.2

Add $- 3$ and $8$ .

$y = 3 x + 5$

Step 5