where is your function ??
That is the product rule, the second equation is the differentiated form of your equation, and in the third Amer is showing you how to do it for any equation.
You take your original equation, reduce the power by 1, multiply the whole thing by the original power, this is the in your equation, and then multiply the whole thing by the derivative of what's in the brackets, in your equation this is .
Hope this helps