# Complementary and Supplementary Angles

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This pdf includes the following topics:-
Recognize complementary and supplementary angles
Supplementary angles
Application of Complementary and Supplementary Angles
Linear Pair
1. 2.2 Complementary and Supplementary Angles
Objective: Recognize complementary and supplementary angles
Complementary angles are:
two angles whose sum is 90 degrees (a right angle)
each of the angles is called the complement of the other.
Example 1: If an angle measures 38 degrees, what is its complement?
90 – 38 = x
x = 52
x⁰
38⁰
An illustration indicating the complement to an angle whose measure is also unknown (x):
If the
Then the complement
angle = x x⁰ to angle x =
(90 – x)⁰
The algebraic expression used to represent a complementary angle is
90 - x
Remember! Complements Right Angle Sum 90
2. Definition
Supplementary angles are:
two angles whose sum is 180 degrees (a straight angle)
each of the two angles is called the supplement of the other
Example 2: If an angle measures 38 degrees, what is the measure of its supplement?
180 – 38 = x
x = 142
x⁰ 38⁰
An illustration indicating the supplement of an angle whose unknown measure = x:
If the Then the supplement
angle = x to angle x =
x⁰ (180 – x)⁰
The algebraic expression used to represent a supplementary angle is:
180 – x
Remember! Supplements Straight Angle Sum 180
To keep from confusing the two, the following logic may help you remember:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
180
90 135
C comes before S in the alphabet, like
90 comes before 180 on a number line!
3. Application of Complementary and Supplementary Angles
Example 3: Problem Solving: If the supplement of an angle is 4 times the measure of its
complement, what is the measure of the
angle? Name Expression Measure
The Angle x
Step 1: Make a table and a diagram! Complement 90 – x
Supplement 180 - x
90 - x 180 - x
x
Step 2: Use the expressions in the table above to help you translate the problem into an
the supplement of an angle is 4 times the measure of its complement
180 - x = 4( 90 – x)
Step 3: Now we have this equation from our second table: 180 – x = 4(90 – x)
solve algebraically
180 – x = 4(90 – x)
180 – x = 360 – 4x (distributed the 4)
3x = 180 (added 4x to each side, and subtracted 180 from each side)
x = 60 (divided both sides by 3)
This solution means “the angle” has a measure of 60 degrees.
Step 4: Fill in the last column of table and answer the question! Sometimes you are asked for
the measure of the complement or supplement, so make sure you re-read the question after finding
all three measures! 
What is the measure of the angle? 60!
Name Expression Measure
The Angle x 60
Complement 90 – x 30
Supplement 180 - x 120
4. Other definitions useful for this section:
Opposite Rays-
Two rays with the same endpoint that extend in opposite directions and make up a straight line.
A
C A B
A
A B C A