Algebra Examples

A line is perpendicular to $y = - \frac{1}{5} x + 1$ and intersects the point $(- 5, 1)$ What is the equation of this perpendicular line?

Step 1

Find the slope when $y = - \frac{1}{5} x + 1$ .

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Step 1.1

Rewrite in slope-intercept form.

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Step 1.1.1

The slope-intercept form is $y = m x + b$ , where $m$ is the slope and $b$ is the y-intercept.

$y = m x + b$

Step 1.1.2

Simplify the right side.

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Step 1.1.2.1

Combine $x$ and $\frac{1}{5}$ .

$y = - \frac{x}{5} + 1$

Step 1.1.3

Write in $y = m x + b$ form.

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Step 1.1.3.1

Reorder terms.

$y = - (\frac{1}{5} x) + 1$

Step 1.1.3.2

Remove parentheses.

$y = - \frac{1}{5} x + 1$

Step 1.2

Using the slope-intercept form, the slope is $- \frac{1}{5}$ .

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

Step 2

The equation of a perpendicular line must have a slope that is the negative reciprocal of the original slope.

$m_{perpendicular} = - \frac{1}{- \frac{1}{5}}$

Step 3

Simplify $- \frac{1}{- \frac{1}{5}}$ to find the slope of the perpendicular line.

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Step 3.1

Cancel the common factor of $1$ and $- 1$ .

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Step 3.1.1

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

$m_{perpendicular} = - \frac{- 1 \cdot - 1}{- \frac{1}{5}}$

Step 3.1.2

Move the negative in front of the fraction.

$m_{perpendicular} = \frac{1}{\frac{1}{5}}$

Step 3.2

Multiply the numerator by the reciprocal of the denominator.

$m_{perpendicular} = 1 \cdot 5$

Step 3.3

Multiply $- - (1 \cdot 5)$ .

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Step 3.3.1

Multiply $5$ by $1$ .

$m_{perpendicular} = - (- 1 \cdot 5)$

Step 3.3.2

Multiply $- 1$ by $5$ .

$m_{perpendicular} = 5$

Step 3.3.3

Multiply $- 1$ by $- 5$ .

$m_{perpendicular} = 5$

Step 4

Find the equation of the perpendicular line using the point-slope formula.

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Step 4.1

Use the slope $5$ and a given point $(- 5, 1)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (1) = 5 \cdot (x - (- 5))$

Step 4.2

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

$y - 1 = 5 \cdot (x + 5)$

Step 5

Solve for $y$ .

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Step 5.1

Simplify $5 \cdot (x + 5)$ .

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Step 5.1.1

Rewrite.

$y - 1 = 0 + 0 + 5 \cdot (x + 5)$

Step 5.1.2

Simplify by adding zeros.

$y - 1 = 5 \cdot (x + 5)$

Step 5.1.3

Apply the distributive property.

$y - 1 = 5 x + 5 \cdot 5$

Step 5.1.4

Multiply $5$ by $5$ .

$y - 1 = 5 x + 25$

Step 5.2

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

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Step 5.2.1

Add $1$ to both sides of the equation.

$y = 5 x + 25 + 1$

Step 5.2.2

Add $25$ and $1$ .

$y = 5 x + 26$

Step 6