Q&A - Ask Doubts and Get Answers
Q

Find the local maxima and local minima, if any, of the following functions. Find also the local maximum and the local minimum values, as the case may be: h(x) = sin x + cos x,

3. Find the local maxima and local minima, if any, of the following functions. Find
also the local maximum and the local minimum values, as the case may be:
(iii) h(x) = \sin x + \cos x,\ 0<x<\frac{\pi}{2}

Answers (1)
Views

Given function is
h(x) = \sin x + \cos x\\ h^{'}(x)= \cos x - \sin x\\ h^{'}(x)= 0\\ \cos x - \sin x = 0\\ \cos x = \sin x\\ x = \frac{\pi}{4} \ \ \ \ \ \ as \ x \ \epsilon \ \left ( 0,\frac{\pi}{2} \right )
Now, we use the second derivative test
h^{''}(x)= -\sin x - \cos x\\ h^{''}(\frac{\pi}{4}) = -\sin \frac{\pi}{4} - \cos \frac{\pi}{4}\\ h^{''}(\frac{\pi}{4}) = -\frac{1}{\sqrt2}-\frac{1}{\sqrt2}\\ h^{''}(\frac{\pi}{4})= -\frac{2}{\sqrt2} = -\sqrt2 < 0
Hence, \frac{\pi}{4}   is the point of maxima and the maximum value is h\left ( \frac{\pi}{4} \right ) which is \sqrt2
 

Exams
Articles
Questions