Posted by **Liz** on Sunday, October 7, 2012 at 10:22pm.

find the derivative of f(x)=3x^2-x using the limit definition.

- CALCULUS help! =) -
**Reiny**, Sunday, October 7, 2012 at 10:26pm
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**, Sunday, October 7, 2012 at 10:58pm
WOW!! You are such a lifesaver!!!!!!!!!=) ...and also very good at math !

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