Answer
$47.4^{\circ}$
Work Step by Step
Use Law of cosines : $a^2=b^2+c^2-2bc \cos A$
This can be re-arranged as: $\cos A=\dfrac{b^2+c^2-a^2}{2bc}$
$\implies \cos A=\dfrac{(17)^2+(8)^2-(13)^2}{2(17)(8)}$
or, $\cos A=\dfrac{184}{272}$
or, $A=47.4^{\circ}$
