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McGraw Hill Integrated II, 2012 View details

5. Isosceles and Equilateral Triangles

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Exercise 31 Page 380

Notice that ∠ ACD and ∠ ACB form a straight angle.

m∠ ACB=136^(∘)

Practice makes perfect

In the previous exercise, we found that m∠ ACD=44^(∘).

As we can see ∠ ACD and ∠ ACB form a straight angle. This means that their measures sum to 180^(∘). Thus, we can find m∠ ACB using the definition of straight angle.

m∠ ACD+m∠ ACB=180

Substitute

m∠ ACD= 44

44+m∠ ACB=180

SubEqn

LHS-44=RHS-44

m∠ ACB=136

As a result, the measure of ∠ ACB is 136^(∘).