Then, we could evaluate the cost function at that temperature.

For example, we could evaluate T ( 5 ) T ( 5 ) to determine the average daily temperature on the 5th day of the year. Thus, we can evaluate the cost function at the temperature T ( d ). For any given day, Cost = C ( T ( d ) ) Cost = C ( T ( d ) ) means that the cost depends on the temperature, which in turns depends on the day of the year. The function T ( d ) T ( d ) gives the average daily temperature on day d d of the year. The function C ( T ) C ( T ) gives the cost C C of heating a house for a given average daily temperature in T T degrees Celsius.

Using descriptive variables, we can notate these two functions. Notice how we have just defined two relationships: The cost depends on the temperature, and the temperature depends on the day. The cost to heat a house will depend on the average daily temperature, and in turn, the average daily temperature depends on the particular day of the year. Suppose we want to calculate how much it costs to heat a house on a particular day of the year. Decompose a composite function into its component functions.Find the domain of a composite function.Create a new function by composition of functions.Combine functions using algebraic operations.

Khan academy precalculus answers