# Homework Help: Limitation first principle method

1. May 28, 2012

### ezsmith

1. The problem statement, all variables and given/known data
Should be a simple question but its really tough for me because my lecturer had never teach me before about x^3

Anyway, the question is find the first derivative by using first principle method :
c) x^3+2x^2+1

2. Relevant equations

3. The attempt at a solution
I did dy/dx = lim h->0 but during the process I am stuck because I am pretty confused about the expand part especially during the power for 3

2. May 28, 2012

### Infinitum

What do you mean by expanding for power 3? Assuming you want to expand (x+h)3, you need to multiply (x+h) thrice Or you can remember the result directly, or you can use the binomial theorem....

Last edited: May 28, 2012
3. May 28, 2012

### ezsmith

Yea, I meant by expanding the (x+h)3. I had managed to solve it using binomial theorem and it has saved me a lot of trouble. Thanks a lot Infinitum. Cheers :)

4. May 28, 2012

### Infinitum

You're welcome!

On a side note,
(a+b)3 is quite a commonly used identity, just like (a+b)2. It will surely help to memorize it.