Trigonometry:
Solving for an Angle
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Formulas:

 

How to set up and solve a trigonometry problem when solving for an angle in the triangle:

 

Example:  In right triangle ABC, leg BC=15 and leg AC=20.
                  Find angle A to the nearest degree.

We will be using the same set up strategy that was discussed on the page
 for solving for the missing side of a right triangle.

Set Up the Diagram Set Up the Formula

Now, divide 15 by 20 to change the fraction into a decimal.

You now need to find an angle whose tangent is 0.75.  To do this, use your scientific or graphing calculator.  (On the scientific calculator, enter 0.75.  You now need to activate the tan-1 key (it is located above the tan key).  To activate this tan-1 key, press 2nd (or shift) and then the tan key.  On the graphing calculator, activate the tan-1 first, and then enter 0.75.)

  rounding as directed.

See how to use your
TI-83+/TI-84+ graphing calculator  with beginning trigonometry.
Click calculator.