It is approximating a derivative:
((x + 0.01)2 - x2)/0.01 → (x2 + 0.02x + 0.0001 - x2)/0.01 → 2x + 0.01
Now if 2x is much bigger than 0.01, then the above is just 2x. If you replace the 0.01 by, say 0.0001, and repeat the process, the result is even closer to just 2x. When you are finding the derivative you replace the 0.01 by, say, h, so you get 2x + h. You then take the limit as h goes to zero, to get the derivative of x2 as exactly 2x.
luv you
