Differentiating f(x) with respect to x, we get

Differentiating f’(x) with respect to x, we get

for minima at x=c, f’(c)=0 and f’’(c)>0

f’(x)=0 ⇒ x³=125 or x=5

f’’(5)=7>0

Hence, x=5 is a point of minima for f(x) and f(5)=75 is the minimum value of (x).