Is there any intuition behind why the derivative of $\cos(x)$ is equal to $-\sin(x)$ or just something to memorize? why is $$\frac{d}{dx}\cos(x)=-\sin(x)$$ I am studying for a differential equation test and I seem to always forget \this, and i am just wondering if there is some intuition i'm missing, or is it just one of those things to memorize? and i know this is not very differential equation related, just one of those things that I've never really understood. 
and alliteratively why is $$ \int\sin(x)dx=-\cos(x)$$
any good explanations would be greatly appreciated. 

Pause before you answer the question. The derivative of sine is (....) cosine. The integral of sine is (....) minus the cosine. The derivative of cosine is (....) minus the sign. The integral of cosine is (...) sine. Never say the answer without the pause. Think of your best reason for the s-i-g-n (several given above, or the cosine curve begins by decreasing), and put that thought into the pause. Thereby train yourself to remember.
