what is the minimum value of 3^ sinx + 3^ cos x. Approach please.

I am not in touch with maths since last few years but i tried may be that can be a possible solution. As we all know to find maxima or minima we have to first differentiate then equate to zero and get the extreme points then we double differentiate it to check wether that point is minima or maxima. So i followed the same way i differentiated it as follows