Exercise 4 Page 425

Two angles are supplementary if the sum of their measures is 180^(∘). Since we are told that ∠3 is a supplement of ∠2, we know that they have the following relationship. m∠ 3 + m∠ 4= 180^(∘) We can find m∠ 4 by substituting the given value, m∠3=148^(∘), into the equation.

m∠ 3 + m∠ 4= 180^(∘)

Substitute

m∠ 3= 148^(∘)

148^(∘)+m∠ 4= 180^(∘)

SubEqn

LHS-148^(∘)=RHS-148^(∘)

m∠ 4= 32^(∘)

The measure of ∠ 4 is 32^(∘).