Page 52 - Math Course 2 (Book 2)

Parallel and Perpendicular Lines

Mo. 8

Lesson 4 Key Concept

Parallel Lines in a Coordination Plane
KEY CONCEPTS:
1. Write an equation of the line that passes Words Two non-vertical lines are parallel if they
through a given point, parallel to a given line have the same slope. All vertical line are
2. Write an equation of the line that passes parallel.
through a given point, perpendicular to a
given line. Model y

same slope
MO. 8 - L4a
0
Identifying Parallel Lines x
vertical lines

Vocabulary A-Z
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parallel lines
Lines in the same plane that do not intersect are Parallel Line Through a Given Point
called parallel lines.

Y Example
1
y = x + 2
2 Write the slope-intercept form of an equation for
2 the line that passes through (4, –2) and is parallel
to the graph of

1 1 y = 1 x – 7
2
Y = x + 1 X
1
2 The line parallel to has the same
x – 7
y =
2
1 2 slope , 1
2
perpendicular lines Replace m with ,and (x, y) with (4, –2) in the
1
Lines that intersect at right angles are called 2
perpendicular lines. same point of slope form.

y – y = m( x – x ) Point-slope form
1 1 1
Y = 2x + 1 y – (–2) = (x – 4) Replace m with y
1
2
3 Y = _ 1 x + 1 2 with –2, and x with 4.
1
2 2 y + 2 = (x – 4) Simplify.
2
1
1 y + 2 = x – 2 Distributive Property
X 2
1
y + 2 –2 = x – 2 – 2 Subtract 2 from each
1 2 3 2 side.

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