Let's say we were trying to take the derivative of the square root of 3x squared minus x. So how could we define an f and a g so that this really is the composition of f of x and g of x? Well, we could define f of x as being equal to the square root of x. And if we defined g of x as being equal to 3x squared minus x, then what is f of g of x? Well, f of g of x is going to be equal to, and I'm going to try to keep all the colors accurate. Hopefully it'll help with the understanding. f of g of x is equal to, where everywhere you see the x, you replace with the g of x, the principal root of g of x, which is equal to the principal root of, we've defined g of x right over here, 3x squared minus x.