So far we have seen how to compute the derivative of a function built up from other functions by addition, subtraction, multiplication and division. There is another very important way that we combine functions: composition. The {{CMD_7}}chain rule{{CMD_8}} allows us to deal with this case. Consider {{MATH_9}} While there are several different ways to differentiate this function, if we let {{MATH_10}} and {{MATH_11}}, then we can express {{MATH_12}}. The question is, can we compute the derivative of a composition of functions using the derivatives of the constituents {{MATH_13}} and {{MATH_14}}? To do so, we need the {{CMD_15}}chain rule{{CMD_16}}.