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 =
1520 34 =
= 0.75,
tan–1 0.75
= m A
Use a calculator.
tan –
ANSWER
So, the measure of A is approximately 36.9o.

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
60.5o b.
m B
= cos –
81.4o

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.
ANSWER
53.1o 2.
Find m D to the nearest tenth of a degree if sin D = 0.54.
ANSWER
32.7o