And I've graphed y is equal to cosine of x in blue and y is equal to sine of x in red. We're not going to prove what the derivatives are, but we're gonna know what they are and get an intuitive sense, and in future videos we'll actually do a proof. So let's start with sine of x. So the derivative can be viewed as a slope of the tangent line. So for example, at this point right over here, it looks like the slope of our tangent line should be zero. So our derivative function should be zero at that x value. Similarly, over here, it looks like the derivative is zero.