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 11 Page 181

What do parallel lines have in common?

y=1/3x-4

Practice makes perfect

When lines are parallel, they have the same slope. To help us identify the slope of this line, let's first convert it into slope-intercept form, y= mx+ b, where m is the slope and (0, b) is the y-intercept.

3y-x=-12
â–¼
Solve for y
3y=x-12
y=x-12/3
y=x/3-12/3
y=1/3x-4

With this, we can more easily identify the slope m and y-intercept b.

y= 1/3x- 4 Now that we have identified the slope, we can write a general equation in slope-intercept form for all lines parallel to the given equation. y= 1/3x+ b We are asked to write the equation of a line parallel to the given equation that passes through the given point ( 18, 2). By substituting this point into the general equation for x and y, we will be able to solve for the y-intercept b of the parallel line.

y=1/3x+b
2=1/3( 18)+b
â–¼
Solve for b
2=6+b
-4=b
b=-4

As we can see we got exactly the same y-intercept as in the given equation. So we can write the equation for the line that is parallel to 3y-x=-12 and passes through (18,2). y= 1/3x- 4