Exercise 19 Page 58

Two angles are complementary if the sum of their measures is 90^(∘). With this in mind, we can create an equation to demonstrate this relationship. m∠ 1 + m∠ 2= 90^(∘) We can find m∠ 2 by substituting the given value, m∠1=12^(∘), into the equation.

m∠ 1 + m∠ 2= 90^(∘)

Substitute

m∠ 1= 12^(∘)

12^(∘) + m∠ 2= 90^(∘)

SubEqn

LHS-12^(∘)=RHS-12^(∘)

m∠ 2= 78^(∘)

The measure of ∠ 2 is 78^(∘).