I was in a lecture in college and my lecturer mentioned the practical reason why the derivative of $ \sin(kx) = k\cos(kx) $. Although I didn't quite understand the reason totally.
Would anyone be able to explain why this derivative is so in practical terms and or logical terms, not with a mathematical proof (i.e. using the chain rule)? I was wondering if you could think of it in terms of the graphs of each of the functions?
I don't really know the reason, therefore any insight/help will be greatly appreciated.
Thank you :-)