CK-12 Foundation
Ck 12: Algebra: Quadratic Functions and Equations
[Free Registration/Login may be required to access all resource tools.] This lesson covers vertex, intercept, and standard forms.
CK-12 Foundation
Ck 12: Algebra: Quadratic Functions and Equations
[Free Registration/Login may be required to access all resource tools.] Recognize a quadratic function as an equation in two variables with a specific form.
University of St. Andrews (UK)
University of St. Andrews: Quadratic, Cubic and Quartic Equations
This site gives a history of quadratic functions.