To determine the angle from a tangent ratio, use the “ tan-1 ” function. Some calculators label this function “arctan”.

Example 2

Determine an angle measure with a tangent ratio of 0.5.

Use the tan-1 function on your calculator.

  • In some calculators you will enter: tan-1 0.5 enter or = .

  • In some calculators you will enter: 0.5 tan-1 = .

If you have entered it correctly into your calculator, you should get an answer of 26.56....

tan-1 0.5 = 26.565...°

Again, it may help to think of this value as part of the table from earlier in the lesson.

20° 0.36 0.36
25° 0.47 0.47
26.565…° 0.5 0.5
30° 0.58 0.58
35° 0.70 0.70

It is essential that you learn how to use the trigonometric functions on your calculator. If you were not able to determine the previous values using your calculator, contact your teacher for assistance.