Answer :

Given: x>0 and xy = 1


We need to find the minimum value of (x + y).










For maximum or minimum value f’(x) = 0.



x = 1 or x =-1


f’’(x) at x = 1.


f’’(x) = 2.


F’’(x)>0 it is decreasing and has minimum value at x = 1


At x = -1


f’’(x) = -2


f’’(x)<0 it is increasing and has maximum value at x = -1.


Substituting x = 1 in f(x) we get


f(x) = 2.


The minimum value of given function is 2.

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