Question

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Answer 1

\[a^2=b^2+c^2-2ab\cos(A)\] solve for \(cos(A)\) and get
\[\cos(A)=\frac{b^2+c^2-a^2}{2bc}\]

Answer 2

then once you find \(\frac{b^2+c^2-a^2}{2bc}\) take the arccosine of that number to find \(A\)

Answer 3

you can do it all in one step
http://www.wolframalpha.com/input/?i=+arccos%28%280.85^2%2B+1.36^2-1.33^2%29%2F%282*.85*1.36%29%29