For the problem f(x)=6x^5/7-x^6/7.

I am getting all the way down to

x^-1/7 = 1/5They are coming up with the answer 78,125. How are they simplifying to that.

f'(x)=6/7 *5x^4-6/7 x^5

f(x) increasing----> let f'(x)>0, 6/7 * x^4 (5-x)>0

6/7 * x^4 is always greater than 0, 5-x>0, x<5

thus on interval 0<x<5, f(x) is increasing

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