Posted by Liz on .
find the derivative of f(x)=3x^2x using the limit definition.

CALCULUS help! =) 
Reiny,
f(x) = 3x^2  x
f(x+h) = 3(x+h)^2  (x+h)
= 3x^2 + 6xh + 3h^2  x  h
dy/dx = lim [ ( f(x+h)  f(x)]/h , as h > 0
= lim (3x^2 + 6xh + 3h^2  x  h  3x^2 + x)/h
= lim (6xh + 3h^2  h)/h
= lim 6x + 3h  1 , as h >0
= 6x  1
(the h> 0 should be under the word "lim" in each line) 
CALCULUS help! =) 
Lizzy,
WOW!! You are such a lifesaver!!!!!!!!!=) ...and also very good at math !