Michael J. answered 10/08/15
Tutor
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Effective High School STEM Tutor & CUNY Math Peer Leader
Difference quotient is defined as
lim f(x + h) - f(x)
h-->0 ______________
h
lim [1 / (x + h)2] - [1 / x2]
h-->0 _____________________
h
Now simplify the difference quotient. Also, due to the fact that zero cannot be in the denominator, you will need to do some factoring and cancelling so the h in the denominator goes away.