Limitation first principle method

[ezsmith]

Homework Statement

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

Homework Equations

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

 

[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...

Edit : Do show your work, it'll be easier to help you out then

 

[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 :)

 

[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.