And this is y is equal to sine of x plus pi over two. Now the visual argument is, all I did is I shifted both of these graphs to the left by pi over two. So it should still be the case that the derivative of the red graph is the blue graph. So we should still be able to say that the derivative with respect to x of the red graph, sine of x plus pi over two, that that is equal to the blue graph. That that is equal to cosine of x plus pi over two. Now what is sine of x plus pi over two? Well, that's the same thing as cosine of x.