Applications Of Derivatives Question 302

Question: If two sides of a triangle be given, then the area of the triangle will be maximum if the angle between the given sides be

Options:

A) $ \frac{\pi }{3} $

B) $ \frac{\pi }{4} $

C) $ \frac{\pi }{6} $

D) $ \frac{\pi }{2} $

Show Answer

Answer:

Correct Answer: D

Solution:

Let a and b are given, then area $ A=\frac{1}{2}ab\sin C $

$ \Rightarrow \frac{dA}{dC}=\frac{1}{2}ab\cos C $

Hence A is maximum, when $ \frac{dA}{dC}=0\Rightarrow C=90{}^\circ $ .