Find the Equation Using Two Points (1,9) , (-2,3)

$(1, 9)$ , $(- 2, 3)$

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.

$m = \frac{3 - (9)}{- 2 - (1)}$

Step 5

Finding the slope $m$ .

Simplify the numerator.

Multiply $- 1$ by $9$ .

$m = \frac{3 - 9}{- 2 - (1)}$

Subtract $9$ from $3$ .

$m = \frac{- 6}{- 2 - (1)}$

Simplify the denominator.

Multiply $- 1$ by $1$ .

$m = \frac{- 6}{- 2 - 1}$

Subtract $1$ from $- 2$ .

$m = \frac{- 6}{- 3}$

Divide $- 6$ by $- 3$ .

$m = 2$

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.

$y = (2) \cdot x + b$

Substitute the value of $x$ into the equation.

$y = (2) \cdot (1) + b$

Substitute the value of $y$ into the equation.

$9 = (2) \cdot (1) + b$

Find the value of $b$ .

Rewrite the equation as $(2) \cdot (1) + b = 9$ .

$(2) \cdot (1) + b = 9$

Multiply $2$ by $1$ .

$2 + b = 9$

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

Subtract $2$ from both sides of the equation.

$b = 9 - 2$

Subtract $2$ from $9$ .

$b = 7$

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.

$y = 2 x + 7$

Step 8

Find the Equation Using Two Points (1,9) , (-2,3)

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