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 !

## Answer this Question

## Related Questions

- calculus - find the limit of f'(x) = 1/(√x) using the limit definition of ...
- calculus - find the limit of f'(x) = 1/(√x) using the limit definition of ...
- calculus - Consider the function. f (x) = 5x3 + 3x (a) Compute the derivative at...
- Calculus Help Please!!! - if f(x)= x+(1/x), find f'(x) using the limit ...
- applied calculus - 3. a) Write out the limit definition for the derivative of y...
- Calculus - y = g(x) = cos(x) Can someone show how to estimate g'(pi/2) using the...
- math - find derivative using limit definition: f(x) = x - sqrt(x) so f'(x) = lim...
- Calculus - 1.) Find the derivative of tan (sec x). 2.) Find the derivative if 1/...
- Calculus derivatives - f(a) = a + √a (a) Find the derivative of the ...
- Calculus - Find the derivative of the function using the definition of a ...

More Related Questions