use the law of cosines to find the side of each triangle. round the answer to nearest tenth.

angle(A ) = 58 degree

side (b) = 9

side (c) =12

find side (a) ?

## law of cosines

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# 1 Answer

use the law of cosines. its pretty straight forward. Usually when you learn the law of cosines you learn that

c^2 = a^2 + b^2 - 2ab cos C. You use this form if you have angle C. If you have angle A, which is what your question is asking, you use:

a^2 = b^2 + c^2 - 2bc cos A

and if you are given angle B then you use:

b^2 = a^2 +c^2 - 2ac cos B

Good luck