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 x^{2}(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......

x^{2}+2xdx+(dx^{2})-(x)^{2}/dx

any explanation of this would be great, cheers