The scientific calculator has a group of keys called the **arc function** keys. The arc function symbol is the **-1** in the upper right corner above the function name.
**The arc function keys display the angle when given the correct function.**

There are three arc function keys on most calculators.

The three other arc functions -- **arc cosecant, arc secant**, and **arc cotangent** -- are also used to find angles, but require another step. For the present, use the three arc function keys on the calculator.

These three functions deal with all three sides of a right triangle, and **Oscar Had A Heap Of Apples** will help you remember these functions.

**Example:**

**First:** Select the reference angle and name the legs.

*Remember *: The right angle is never used as the reference angle.

**Second:** Look at the functions chart and choose the function that corresponds to the known sides of the triangle.
Since we know the lengths of all the sides of the above triangle, any of the functions can be used.

Let's use the **sine** function,

**Third:** Assign the numbers to the ratio and calculate the problem.

**Fourth:** Use the correct arc function key to find the degrees of the reference angle.
The key is used to find the degrees of this reference angle.

(In rounding off degrees to the nearest 1/2 degree, from 0.00 to 0.249, go down to 0. From 0.25 to .749, go to .5° . From .75 to .99, go to 1° .)

As you can see, the arc function keys react to whatever is in the display. Below, enter each number and look at the function to determine which arc function key to use, and push that key.

**Finding the Angles Practice:**

Find the angle for each function. Round off to the nearest 1/2° .

(1) sin = 0.3745 (5) tan = 0.5785
(2) tan = 1 (6) sin = 0.7756
(3) cos = 0.8632 (7) cos = 0.9397
(4) sin = 1 (8) tan 1.5030