You must apply the chain rule whenever you see a function contained within another function. For example, if you were to differentiate (sin x)2 you would apply the chain rule as the sin function exists inside the brackets. You would apply the product rule whenever you differentiate something which consists of two functions multiplied together, eg... x2ex would require use of the product rule as the function x2 is multiplied by ex. Finally, the quotient rule would be applied in the case where you need to differentiate a function in which one function is divided by another function, eg... 4x2/cos x would be diferentiated using the chain rule as 4x2 is being divided by cos x.