Posted by **Sara** on Sunday, January 17, 2010 at 11:08am.

If given an a cos, sin, or tan of an angle of a right triangle, what steps would you take on your calculator to find the measure of that angle? (For example: cos A = .7986, find angle A, The opposite side is 3. The hypotnuse is 5. And the adjacent side is 4)

If someone would just explain what to do with a graphing calculator (TI-84), that would mean a lot! thanks

- geometry -
**drwls**, Sunday, January 17, 2010 at 11:20am
You write:

"For example: cos A = .7986, find angle A, The opposite side is 3. The hypotenuse is 5. And the adjacent side is 4"

but for a 3:4:5 triangle, the cosine is 0.8.

I don't have your calculator, but what you need is a cos^-1 or arc cosine key.

If cosA = 0.7986, A = cos^-1 0.7986 = 37.003 degrees.

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