1. 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 = 15 20 3434 == 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 36.9 o.

2. 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 60.5 o b. m B = cos –1 0.15 81.4 o

3. 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 SOLUTION Because tan C = 20 15 4343 == 1.333, tan –1 1.33 = m C Use a calculator tan –1 1.33 53.1°

4. GUIDED PRACTICE for Examples 1, and 2 2. Find m D to the nearest tenth of a degree if sin D = 0.54. SOLUTION a. m D = sin –1 0.54 32.7°