Candace opened her math book and discovered this dilemma.
The two angles below are complementary.
Candace is puzzled. Are you? Using equations and geometry can help you figure this one out. Pay attention and you will learn all that you need to know from this Concept.
Guidance
Let's think about angle pairs. There are different types of angle pairs.

Supplementary angles are two angles that form a straight line, and their sum is always
180∘ . 
Complementary angles together form a right angle and have a sum of
90∘ . 
Adjacent angles are next to each other. When they form a line, their sum is
180∘ .  Vertical angles are directly opposite each other. They are equal.
Take a look at this situation involving angle pairs.
Fill in the figure below with the angle measures for all of the angles shown.
First, notice that we only have one angle to go on. This angle measures 70 degrees. However, that is enough information to figure out all of the other angles in this diagram. We can use the information that we know about angles to figure the measures of these angles out.
Let’s begin with adjacent angles. Angle
We can write this equation.
We know that
Next, we can work on the vertical angles. Angle
Angle
Using our known information, we have figured out the measures of all of the missing angles.
Find the measure of an angle that forms a supplementary angle with
Example A
Solution:
Example B
Solution:
Example C
Solution:
Now let's go back to the dilemma from the beginning of the Concept.
If the two angles are complementary, then we know that the sum of the two angles is 90 degrees.
Let's write an equation to show that.
Now we can solve for
This is the answer.
Vocabulary
 Parallel lines
 lines that are an equal distance apart and will never intersect.
 Intersecting lines
 lines that cross at one point.
 Perpendicular lines

lines that intersect at a
90∘ angle and form two or more90∘ angles.
 Angle
 the measure of the space formed by two intersecting lines.
 Straight angle

is a straight line equal to
180∘ .
 Angle Pairs
 the relationship formed by two angles.
 Complementary Angles

two angles whose sum is
90∘ .
 Supplementary Angles

two angles whose sum is
180∘ .
 Adjacent Angles
 angles that are next to each other.
 Vertical Angles
 angles that are diagonally across from each other.
Guided Practice
Here is one for you to try on your own.
A pair of angles are adjacent and complementary. What is the missing measure if
Solution
To figure this out, you have to know a few things. First, adjacent angles are next to each other and complementary angles have a sum of
Knowing this, we can write an equation.
Now we can solve for
The measure of
Video Review
Complementary, Supplementary and Vertical Angles
Practice
Directions: If the following angle pairs are complementary, then what is the measure of the missing angle?

∠A∠B=45∘=? 
∠C∠D=83∘=? 
∠E∠F=33∘=? 
∠G∠H=53∘=?
Directions: If the following angle pairs are supplementary, then what is the measure of the missing angle?

∠A∠B=40∘=? 
∠A∠B=75∘=? 
∠C∠F=110∘=? 
∠D∠E=125∘=? 
∠M∠N=10∘=? 
∠O∠P=157∘=?
Directions: Define the following types of angle pairs.
 Vertical angles
 Adjacent angles
 Complementary angles
 Supplementary angles
 Interior angles