Let's keep trying this. So over here, cosine of x, it looks like the slope of the tangent line is negative one. And so we would want the derivative to go through that point right over there. All right, this is starting to seem, it doesn't seem like the derivative of cosine of x could be sine of x. In fact, this is the opposite of what sine of x is doing. Sine of x is at one, not negative one at that point. But that's an interesting theory.