Question

In right triangle ABC, ∠A and ∠B are complementary angles and sin A = 89. What is cos B?

Answer 1

8√17/17
8/9
√17/9
√17/8

Answer 2

cos B = 0.89

Explanation:

If ∠A and ∠B are complementary then: ∠A + ∠B = 90°

Given that sin A = 8/9 then A can be computed with the inverse of sine as follows:

∠A = arcsin(8/9) = 62.7°

Then:

62.7° + ∠B = 90°

∠B = 90° - 62.7°

∠B = 27.3°

Finally,

cos 27.3° = 0.89