Originally Posted by
Jhevon i guess you can prove it using the limit definition of a derivative, but i don't remember if that's the way i was taught it. it's actually a well-known fact that everyone just takes for granted. it's like saying the derivative of sine is cosine, no one asks how that is, because its so common. derivatives of arcsine, arccos, arctan, etc should be in the back of your calculus book or wherever the formula page is, check it out. if you're still skeptical, try the limit definition to prove it (there may be an easier way, don't remember).