# Trig question

How do you go about finding the arctangent of an unfamiliar number. Example, arctan (-2)? I think it's in the direction of half-angles and double angels, but how do I get the angle to start with the formulas in the first place?

Thanks in advance!

## Answers and Replies

If x = arctan(-2), then tan(x) = -2. I don't think double or half-angle will help you for this problem. Sometimes you can figure out what x is, sometimes you can't without a calculator.

berkeman
Mentor
How do you go about finding the arctangent of an unfamiliar number. Example, arctan (-2)? I think it's in the direction of half-angles and double angels, but how do I get the angle to start with the formulas in the first place?

Thanks in advance!

I like to visualize the plots of sin, cos, and tan, to help me with problems like this. Draw the tan function, including the asymptotes and the repeating pattern. The arctan is just that plot turned on its side, but without the repeating patterns (because that would give you multiple values for arctan).

http://en.wikipedia.org/wiki/Arctan

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