limx->0 cosx-1/2x
ok i kinda dont know where to start
Alternatively, one could just use the definition of the derivative.
I guess this is probably begging the question a little bit, though, since we effectively need to know this limit to calculate the derivatives of sin and cos in the first place. If you already have as and you are working with the geometric definitions (not the power series definitions), then Prove It's proof seems best so far.