Question 58

For an acute angle $$\theta, \sin \theta + \cos \theta$$ takes the greater value when $$\theta$$ is

Solution

Let $$f(\theta)=sin\theta+cos\theta$$

=> $$f'(\theta)=cos\theta-sin\theta$$

Now, max value of $$f(\theta)$$ will be when $$f'(\theta)=0$$

=> $$cos\theta=sin\theta$$

$$\because \theta$$ is acute, => $$\theta=45^\circ$$

=> Ans - (B)

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