Differentiate using the chain rule, which states that is where and .
To apply the Chain Rule, set as .
The derivative of with respect to is .
Replace all occurrences of with .
Since is constant with respect to , the derivative of with respect to is .
Differentiate using the Power Rule which states that is where .
Simplify the expression.
Multiply by .
Reorder the factors of .
Find the Derivative – d/dx cos(kx)