Algebra Examples

Find the equation of a line perpendicular to $y = - 4 x$ that contains the point $(- 3, - 4)$

Step 1

Write the problem as a mathematical expression.

$y = - 4 x$ , $(- 3, - 4)$

Step 2

Use the slope-intercept form to find the slope.

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Step 2.1

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 2.2

Using the slope-intercept form, the slope is $- 4$ .

$m = - 4$

Step 3

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

$m_{perpendicular} = - \frac{1}{- 4}$

Step 4

Simplify $- \frac{1}{- 4}$ to find the slope of the perpendicular line.

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Step 4.1

Move the negative in front of the fraction.

$m_{perpendicular} = \frac{1}{4}$

Step 4.2

Multiply $- - \frac{1}{4}$ .

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Step 4.2.1

Multiply $- 1$ by $- 1$ .

$m_{perpendicular} = 1 (\frac{1}{4})$

Step 4.2.2

Multiply $\frac{1}{4}$ by $1$ .

$m_{perpendicular} = \frac{1}{4}$

Step 5

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

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Step 5.1

Use the slope $\frac{1}{4}$ and a given point $(- 3, - 4)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (- 4) = \frac{1}{4} \cdot (x - (- 3))$

Step 5.2

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

$y + 4 = \frac{1}{4} \cdot (x + 3)$

Step 6

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

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Step 6.1

Solve for $y$ .

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Step 6.1.1

Simplify $\frac{1}{4} \cdot (x + 3)$ .

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Step 6.1.1.1

Rewrite.

$y + 4 = 0 + 0 + \frac{1}{4} \cdot (x + 3)$

Step 6.1.1.2

Simplify by adding zeros.

$y + 4 = \frac{1}{4} \cdot (x + 3)$

Step 6.1.1.3

Apply the distributive property.

$y + 4 = \frac{1}{4} x + \frac{1}{4} \cdot 3$

Step 6.1.1.4

Combine $\frac{1}{4}$ and $x$ .

$y + 4 = \frac{x}{4} + \frac{1}{4} \cdot 3$

Step 6.1.1.5

Combine $\frac{1}{4}$ and $3$ .

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

Step 6.1.2

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

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Step 6.1.2.1

Subtract $4$ from both sides of the equation.

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

Step 6.1.2.2

To write $- 4$ as a fraction with a common denominator, multiply by $\frac{4}{4}$ .

$y = \frac{x}{4} + \frac{3}{4} - 4 \cdot \frac{4}{4}$

Step 6.1.2.3

Combine $- 4$ and $\frac{4}{4}$ .

$y = \frac{x}{4} + \frac{3}{4} + \frac{- 4 \cdot 4}{4}$

Step 6.1.2.4

Combine the numerators over the common denominator.

$y = \frac{x}{4} + \frac{3 - 4 \cdot 4}{4}$

Step 6.1.2.5

Simplify the numerator.

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Step 6.1.2.5.1

Multiply $- 4$ by $4$ .

$y = \frac{x}{4} + \frac{3 - 16}{4}$

Step 6.1.2.5.2

Subtract $16$ from $3$ .

$y = \frac{x}{4} + \frac{- 13}{4}$

Step 6.1.2.6

Move the negative in front of the fraction.

$y = \frac{x}{4} - \frac{13}{4}$

Step 6.2

Reorder terms.

$y = \frac{1}{4} x - \frac{13}{4}$

Step 7