Exercise 15 Page 440

We know that ∠ 1 and an angle that measures 50^(∘) are supplementary. Then, the sum of their measures is 180^(∘). m∠ 1 + 50^(∘) = 180^(∘) We can solve this equation for m∠ 1 to the measure of ∠ 1.

m∠ 1 +50^(∘)=180^(∘)

SubEqn

LHS-50^(∘)=RHS-50^(∘)

m∠ 1 - 50^(∘)=180^(∘)-50^(∘)

SubTerm

Subtract term

m∠ 1= 130 ^(∘)

We found that the measure of ∠ 1 is 130^(∘). We are told that there are another angle that measures 50^(∘) and ∠ 3 are also supplementary. m∠ 3 + 50^(∘) = 180^(∘) Let's solve this equation to find the measure of ∠ 3.

m∠ 3 +50^(∘)=180^(∘)

SubEqn

LHS-50^(∘)=RHS-50^(∘)

m∠ 3 - 50^(∘)=180^(∘)-50

SubTerm

Subtract term

m∠ 3= 130 ^(∘)

The measure of ∠ 3 is 130^(∘). This means that m∠ 1 and m∠ 3 are equal.