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How do you do inverse trig without calculator?

For example,the first problem on my worksheet is SAS, and I'm trying to find the angle using two side lengths. The first side is adjacent to the angle, and the other side is the hypotenuse,so I used cosine.

8 over 10 = 0.8

0.8 = Cos[x]

x = Cos^-1[0.8]

a}Is this the right process?

b} To find the answer, I look for the same number in sin?

Thanks in advance!

1 Answer

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  • Anonymous
    8 years ago
    Favorite Answer

    a) that is correct

    b) You need a calculator to find the arccosine of .8, that is until you get to Calculus. At that point one can use series expansions or other approximation methods - but in practice everyone uses a calculator. It is not something you can calculate easily by hand until Calculus (and even then it is tedius).

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