EXAMPLE 1 Use an inverse tangent to find an angle measure Use a calculator to approximate the measure of A to the nearest tenth of a degree. SOLUTION Because tan A = 1520 34 = = 0.75, tan–1 0.75 = m A Use a calculator. tan –1 0.75 36.86989765. . . ANSWER So, the measure of A is approximately 36.9o.
EXAMPLE 2 Use an inverse sine and an inverse cosine Let A and B be acute angles in a right triangle. Use a calculator to approximate the measures of A and B to the nearest tenth of a degree. a. sin A = 0.87 b. cos B = 0.15 SOLUTION a. m A = sin –1 0.87 60.5o b. m B = cos –1 0.15 81.4o
GUIDED PRACTICE for Examples 1 and 2 1. Look back at Example 1. Use a calculator and an inverse tangent to approximate m C to the nearest tenth of a degree. ANSWER 53.1o 2. Find m D to the nearest tenth of a degree if sin D = 0.54. ANSWER 32.7o