Precalculus Examples

$(3, 1)$ , $(9, 6)$

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.

$m = \frac{6 - (1)}{9 - (3)}$

Step 5

Finding the slope $m$ .

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Step 5.1

Simplify the numerator.

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Step 5.1.1

Multiply $- 1$ by $1$ .

$m = \frac{6 - 1}{9 - (3)}$

Step 5.1.2

Subtract $1$ from $6$ .

$m = \frac{5}{9 - (3)}$

Step 5.2

Simplify the denominator.

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Step 5.2.1

Multiply $- 1$ by $3$ .

$m = \frac{5}{9 - 3}$

Step 5.2.2

Subtract $3$ from $9$ .

$m = \frac{5}{6}$

Step 6

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

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Step 6.1

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

$y = m x + b$

Step 6.2

Substitute the value of $m$ into the equation.

$y = (\frac{5}{6}) x + b$

Step 6.3

Substitute the value of $x$ into the equation.

$y = (\frac{5}{6}) \cdot (3) + b$

Step 6.4

Substitute the value of $y$ into the equation.

$1 = (\frac{5}{6}) \cdot (3) + b$

Step 6.5

Find the value of $b$ .

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Step 6.5.1

Rewrite the equation as $\frac{5}{6} \cdot 3 + b = 1$ .

$\frac{5}{6} \cdot 3 + b = 1$

Step 6.5.2

Cancel the common factor of $3$ .

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Step 6.5.2.1

Factor $3$ out of $6$ .

$\frac{5}{3 (2)} \cdot 3 + b = 1$

Step 6.5.2.2

Cancel the common factor.

$\frac{5}{3 \cdot 2} \cdot 3 + b = 1$

Step 6.5.2.3

Rewrite the expression.

$\frac{5}{2} + b = 1$

Step 6.5.3

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

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Step 6.5.3.1

Subtract $\frac{5}{2}$ from both sides of the equation.

$b = 1 - \frac{5}{2}$

Step 6.5.3.2

Write $1$ as a fraction with a common denominator.

$b = \frac{2}{2} - \frac{5}{2}$

Step 6.5.3.3

Combine the numerators over the common denominator.

$b = \frac{2 - 5}{2}$

Step 6.5.3.4

Subtract $5$ from $2$ .

$b = \frac{- 3}{2}$

Step 6.5.3.5

Move the negative in front of the fraction.

$b = - \frac{3}{2}$

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.

$y = \frac{5}{6} x - \frac{3}{2}$

Step 8