Posted by **NaNa** on Thursday, October 11, 2007 at 1:09am.

Use the definition of the derivative to find f'(x)

1. f(x) 2x^2 + x - 1

Before the final step, my 'result' looked weird and I think I did something wrong in my arithmetic...someone correct me?

Here's my work...

BEGINNING STEP:

lim [2(x + deltaX)^2 - (x + deltaX) - (2x^2 + x - 1)] / deltaX

near the end step:

lim [4x + 2deltaX - 2x^2 - 1] / deltaX

Thanks

- Calculus - need help! -
**Quidditch**, Thursday, October 11, 2007 at 1:41am
You started correctly, but you must have a math error in the intermediate steps.

((2(x+deltaX)^2 + (x+deltaX) - 1) - (2x^2 + x - 1) )/deltaX

=((2x2+4(x*deltaX) + 2deltaX^2 + x + deltaX - 1) - (2x^2 + x - 1) ) /deltaX

=(4(x*deltaX) + 2*deltaX^2 + deltaX)/deltaX

=4x + deltaX + 1

limit as delatX goes to 0

=4x + 1

- Calculus - need help! -
**Quidditch**, Thursday, October 11, 2007 at 2:05am
Ooops!

the step before the limit statement should have read:

4x + 2deltaX + 1

## Answer This Question

## Related Questions

- calculus - I need a step-by-step limit definition of derivative for y = ln(x).
- Derivative - I need to find the derivative of (x) / (x^2 +1) I got x^2 + 1(1) - ...
- calculus - I posted one before but this is another one of those problems that i ...
- Pre-calculus. - Wesley and Delia are playing a math game. Wesley gives Delia ...
- calculus - Find the derivative of the function using the definition of ...
- calculus - find the derivative of f(x)=x^2sec^2(3x) also with g(x)=sqrt(cosxsecx...
- College Calculus 1 - We have to find the first and second derivative of f(x)=x^(...
- Calculus - If x = t^2 + 1 and y = t^3, then d^2y/dx^2 = I know I can solve for t...
- Maths (Simultaneous equations) - You know f(x)= ax˛ + bx + c. Well when you get ...
- calculus - f(x)=1/x^2 use formal definition of derivative to find slope at x=2

More Related Questions