Find the Equation Using Two Points (-4,2) , (4,8)

$(- 4, 2)$ , $(4, 8)$

Step 1

Use $y = m x + b$ to calculate the equation of the line, where $m$ represents the slope and $b$ represents the y-intercept.

To calculate the equation of the line, use the $y = m x + b$ format.

Step 2

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 3

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 4

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

$m = \frac{8 - (2)}{4 - (- 4)}$

Step 5

Finding the slope $m$ .

Reduce the expression by cancelling the common factors.

Cancel the common factor of $8 - (2)$ and $4 - (- 4)$ .

Rewrite $8$ as $- 1 (- 8)$ .

$m = \frac{- 1 \cdot - 8 - (2)}{4 - (- 4)}$

Factor $- 1$ out of $- 1 (- 8) - (2)$ .

$m = \frac{- 1 (- 8 + 2)}{4 - (- 4)}$

Reorder terms.

$m = \frac{- 1 (- 8 + 2)}{4 - 4 \cdot - 1}$

Factor $2$ out of $- 1 (- 8 + 2)$ .

$m = \frac{2 (- 1 (- 4 + 1))}{4 - 4 \cdot - 1}$

Cancel the common factors.

Factor $2$ out of $4$ .

$m = \frac{2 (- 1 (- 4 + 1))}{2 (2) - 4 \cdot - 1}$

Factor $2$ out of $- 4 \cdot - 1$ .

$m = \frac{2 (- 1 (- 4 + 1))}{2 (2) + 2 (- 2 \cdot - 1)}$

Factor $2$ out of $2 (2) + 2 (- 2 \cdot - 1)$ .

$m = \frac{2 (- 1 (- 4 + 1))}{2 (2 - 2 \cdot - 1)}$

Cancel the common factor.

$m = \frac{2 (- 1 (- 4 + 1))}{2 (2 - 2 \cdot - 1)}$

Rewrite the expression.

$m = \frac{- 1 (- 4 + 1)}{2 - 2 \cdot - 1}$

Add $- 4$ and $1$ .

$m = \frac{- 1 \cdot - 3}{2 - 2 \cdot - 1}$

Simplify the denominator.

Multiply $- 2$ by $- 1$ .

$m = \frac{- 1 \cdot - 3}{2 + 2}$

Add $2$ and $2$ .

$m = \frac{- 1 \cdot - 3}{4}$

Multiply $- 1$ by $- 3$ .

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

Step 6

Find the value of $b$ using the formula for the equation of a line.

Use the formula for the equation of a line to find $b$ .

$y = m x + b$

Substitute the value of $m$ into the equation.

$y = (\frac{3}{4}) x + b$

Substitute the value of $x$ into the equation.

$y = (\frac{3}{4}) \cdot (- 4) + b$

Substitute the value of $y$ into the equation.

$2 = (\frac{3}{4}) \cdot (- 4) + b$

Find the value of $b$ .

Rewrite the equation as $\frac{3}{4} \cdot - 4 + b = 2$ .

$\frac{3}{4} \cdot - 4 + b = 2$

Simplify each term.

Cancel the common factor of $4$ .

Factor $4$ out of $- 4$ .

$\frac{3}{4} \cdot (4 (- 1)) + b = 2$

Cancel the common factor.

$\frac{3}{4} \cdot (4 \cdot - 1) + b = 2$

Rewrite the expression.

$3 \cdot - 1 + b = 2$

Multiply $3$ by $- 1$ .

$- 3 + b = 2$

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

Add $3$ to both sides of the equation.

$b = 2 + 3$

Add $2$ and $3$ .

$b = 5$

Step 7

Now that the values of $m$ (slope) and $b$ (y-intercept) are known, substitute them into $y = m x + b$ to find the equation of the line.

$y = \frac{3}{4} x + 5$

Step 8

Find the Equation Using Two Points (-4,2) , (4,8)

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