Question

Triangle ABC, m/A = 15°, a = 9, and b = 12. Find c

Answer 1

Check the picture below.

`\cfrac{\sin(15^o)}{9}=\cfrac{\sin(B)}{12}\implies \cfrac{12\sin(15^o)}{9}=\sin(B)\implies \sin^(-1)\left( \cfrac{12\sin(15^o)}{9} \right)=B \\\\\\ 20.19^o\approx B\hspace{12em}\stackrel{180-20.19-15}{C\approx 144.81^o} \\\\[-0.35em] ~\dotfill\\\\ \cfrac{\sin(15^o)}{9}=\cfrac{\sin(144.81^o)}{c}\implies c=\cfrac{9\sin(144.81^o)}{\sin(15^o)}\implies \boxed{c\approx 20.0}`