If we look right over here on sine of x, it looks like the slope of the tangent line would be pretty close to one. If that is the case, then in our derivative function, when x is equal to zero, that derivative function should be equal to one. Similarly, over here, it looks like the slope of the tangent line is negative one, which tells us that the derivative function should be hitting the value of negative one at that x value. So you're probably seeing something interesting emerge. Everywhere, while we're trying to plot the slope of the tangent line, it seems to coincide with y is equal to cosine of x. And it is indeed the case that the derivative of sine of x is equal to cosine of x. And you can see that it makes sense not just at the points we tried, but even in the trends.