# Thread: Stuck finding the derivative of x^2 using difference quotient

1. ## Stuck finding the derivative of x^2 using difference quotient

Hey id be greatful to anyone who can help me with this which i guess is easy but im too dumb to get...

Whilst finding the derivative of x2 (using the difference quotient) it is at this step that i get confused and need help on...

f'(x)= (x+dx)2-(x)2/dx

how do they get from the above equation to......

x2+2xdx+(dx2)-(x)2/dx

any explanation of this would be great, cheers

2. ## Re: Stuck finding the derivative of x^2 using difference quotient

Originally Posted by fwp0406
Hey id be greatful to anyone who can help me with this which i guess is easy but im too dumb to get...

Whilst finding the derivative of x2 (using the difference quotient) it is at this step that i get confused and need help on...

f'(x)= (x+dx)2-(x)2/dx

how do they get from the above equation to......

x2+2xdx+(dx2)-(x)2/dx

any explanation of this would be great, cheers
Expand the brackets.

3. ## Re: Stuck finding the derivative of x^2 using difference quotient

$\displaystyle (a+ b)^2= a^2+ 2ab+ b^2$ so that $\displaystyle (x+ dx)^2= x^2+ 2(x)(dx)+ (dx)^2$.