Big Ideas Math: Modeling Real Life, Grade 7
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5. Finding Unknown Angle Measures
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Exercise 9 Page 392

What is the sum of the measures of two complementary angles?

x=18

Practice makes perfect
First, let's take a look at the given diagram.
We have been given a pair of complementary angles and their measures written as algebraic expressions. Since the angles are complementary, we know that the sum of their measures should equal 90^(∘). We can solve for x by creating an equation using the expressions for the two smaller angles and their sum.
4x^(∘) + x^(∘) = 90^(∘)
5x^(∘) = 90^(∘)
x^(∘) = 18^(∘)