The average temperature around the Tropic of Cancer for a particular day in January can be modeled using the equation above, where T is the temperature in degrees Celsius and d is the number of days after January 1 (on January 1, d=0). According to this model, what is the lowest average temperature, in degrees Celsius, for a day in January, which has 31 days?
The expression for temperature is already in vertex form: T=a(d−d subscript 0)^2+T subscript 0. The vertex of this quadratic function occurs at (15,20).
