A) \[\frac{\pi }{2}\]
B) \[\frac{3\pi }{2}\]
C) \[\frac{2\pi }{3}\]
D) \[\frac{\pi }{3}\]
Correct Answer: C
Solution :
Let \[a=13,\,\,b=7,\,\,c=8\] \[\therefore \] \[\cos A=\frac{{{b}^{2}}+{{c}^{2}}-{{a}^{2}}}{2bc}=\frac{{{(7)}^{2}}+{{(8)}^{2}}-{{(13)}^{2}}}{2\times 7\times 8}\] \[=\frac{49+64-169}{112}=-\frac{1}{2}\] \[\Rightarrow \] \[A=\frac{2\pi }{3}\]
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