The arctan function represent the inverse of the tangent function. If the tangent of a number is a second number, the arctan of the second number is the first number. The function is useful when solving trigonometric problems. If you know the two shorter lengths in a rightangled triangle, the arctan of the ratio between them equals the angle between one of them and the hypotenuse.
Things You'll Need
 Scientific calculator

Search your calculator for the arctan button, which will be marked as either "arctan," "atan" or "tan1." If the calculator has an arctan button, press it and skip to Step 3. If it doesn't, continue to Step 2.

Press the calculator's "shift," "2nd" or "function" key, and then press the "tan" key.

Type the number whose arctan you want to find. For this example, type in the number "0.577."

Press the "=" button. The number's arctan will appear. The arctan of 0.577, for instance, is approximately 30.
References
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