Quadratic Models (DP IB Applications & Interpretation (AI)): Revision Note

Quadratic Models

What are the parameters of a quadratic model?

• A quadratic model is of the form 

• The c represents the value of the function when x = 0

  • This is the value of the function when the independent variable is not present

  • This is usually referred to as the initial value

• The a has the biggest impact on the rate of change of the function

  • If a has a large absolute value then the rate of change varies rapidly

  • If a has a small absolute value then the rate of change varies slowly

• The maximum (or minimum) of the function occurs when 

  • This is given in the formula booklet as the axis of symmetry

What can be modelled as a quadratic model?

• If the graph of the data resembles a  or  shape

• These can be used if the graph has a single maximum or minimum

  • H(t) is the vertical height of a football t seconds after being kicked

  • A(x) is the area of rectangle of length x cm that can be made with a 20 cm length of string

What are possible limitations of a quadratic model?

• A quadratic has either a maximum or a minimum but not both

  • This means one end is unbounded

  • In real-life this might not be the case

  • The function might have both a maximum and a minimum

  • To overcome this you can decide on an appropriate domain so that the outputs are within a range

• Quadratic graphs are symmetrical

  • This might not be the case in real-life