If you said natural log of x is f of x and sine of x is g of x, this is the product of sine and g of x. This is the product of f of x and g of x. And here you would use the product rule. So to actually compute this, you would use the product, the product rule. But this is a composition. Here you have f of g of x, not f of x times g of x. So here you have, that is our g of x, it equals sine of x.