Big Ideas Math Integrated I, 2016
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Big Ideas Math Integrated I, 2016 View details
3. Writing Equations of Parallel and Perpendicular Lines
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Exercise 4 Page 179

What similarities and differences do perpendicular lines have?

y=1/3x+6

Practice makes perfect

To write the equation of a line perpendicular to the given equation, we first need to determine its slope. After that, we will write a general equation and use the given point to determine the y-intercept.

Calculating the Perpendicular Line's Slope

Two lines are perpendicular when their slopes are negative reciprocals. This means that the product of a given slope and the slope of a line perpendicular to it will be -1. m_1*m_2=-1 For any equation written in slope-intercept form, y=mx+ b, we can identify its slope as the value of m. y=-3x -1 In the given equation, we can see that its slope is -3. By substituting this value into our negative reciprocal equation for m_1, we can solve for the slope of the perpendicular line, m_2.

m_1 * m_2 = - 1
-3* m_2 = - 1
â–¼
Solve for m_2
-3m_2=-1
m_2 = 1/3

With this, we can identify that any line perpendicular to the given equation will have a slope of 13.

Writing the Perpendicular Line's Equation

With the slope m_2=13, we can write a general equation in slope-intercept form for all lines perpendicular to the given equation. y=1/3x+b By substituting the given point ( -3, 5) into this equation for x and y, we can solve for the y-intercept b of the perpendicular line.

y=1/3x+b
5=1/3( -3)+b
â–¼
Solve for b
5=-1+ b
6=b
b=6

Now that we have the y-intercept, we can write the equation for the line that is perpendicular to y=-3x-1 and passes through the point (-3,5). y=1/3x+6