Cosine Rule (missing side)
\( a^2=b^2+c^2-2bcCosA\)
Find x (to 2 d.p.)
5
8
x
20°
\begin{align} x^2 & = 5^2+8^2-2(5)(8)Cos(20^{\circ}) \\ \\ & = 25+64-80(0.939)\\ \\ & = 13.88 \\ \\ \implies \ x & = 3.73\ (to\ 2\ d.p.) \end{align}