Let f(x) = x².
a) Use the definition of derivative to find f'(x).
b) Use the definition of derivative to find f''(x).

a) f'(x) = lim(h -> 0) ((x + h)² - x²) / h
b) f''(x) = lim(h -> 0) (((x + h)² - x²) - ((x + h) - x)) / h