In general, do not use any derivative rules ( as power rule,
etc.). Find the derivative of the following functions at the point
"a" by computing average rate of changes for h = ±1, ±0.1, ±0.01,
±0.001, ±0.0001 :
a.) f(x) = x2 + x3 , a = 1
b.) f(x) = x 2+ x3 , a = 3
c.) . f(x) = x − x2 , a = 2