# NEW USER NEED SUM HELP with this calculus prob. Derivative Prob.

• Jun 24th 2013, 05:13 AM
iamjhay
NEW USER NEED SUM HELP with this calculus prob. Derivative Prob.
hi im jhay from.. phl. civil engr. student .. first time to take calculus..
can u explain to me step by step of finding the derivative of a function x√(x-1) using four step rule .. big tnx in advance..(Evilgrin)
• Jun 24th 2013, 05:16 AM
Prove It
Re: NEW USER NEED SUM HELP with this calculus prob. Derivative Prob.
I don't know what you mean by the "four step rule". It is a product of two functions, so use the product rule. The second function also needs the use of the chain rule.
• Jun 24th 2013, 10:01 AM
hollywood
Re: NEW USER NEED SUM HELP with this calculus prob. Derivative Prob.
I think these are the four steps that iamjhay is talking about:

1. Write $\displaystyle f(x+h)$ and $\displaystyle f(x)$

2. Compute $\displaystyle f(x+h) - f(x)$

3. Simplify $\displaystyle \frac{f(x+h)-f(x)}{h}$

4. Find $\displaystyle \lim_{h\to0}\frac{f(x+h)-f(x)}{h}$

We would call it computing the derivative from the definition.

To iamjhay: I think this identity will get you over the difficult part:

$\displaystyle \sqrt{a}-\sqrt{b}=\frac{a-b}{\sqrt{a}+\sqrt{b}}$

If you're still having trouble, show us the work you've done so far and we'll help you with the next step.

- Hollywood