We know that the derivative with respect to x of cosine of x is equal to negative sine of x. And so what we want to do in this video is find the derivatives of the other basic trig functions. So in particular, we know, let's figure out what the derivative with respect to x, let's first do tangent of x. Tangent of x. Well, this is the same thing as trying to find the derivative with respect to x of, well, tangent of x is just sine of x. Sine of x over cosine of x. And since it can be expressed as the quotient of two functions, we can apply the quotient rule here to evaluate this or to figure out what this is going to be. The quotient rule tells us that this is going to be the derivative of the top function, which we know is cosine of x, times the bottom function, which is cosine of x, so times cosine of x, minus the top function, which is sine of x, the top function, which is sine of x, sine of x, times the derivative of the bottom function, so the derivative of cosine of x is negative sine of x.