Windstream
Ojk World of Math: Relationships Between the Functions
This tutorial discusses relationships among all the trig identities. Examples are given on how to apply them to simplify trig expressions and prove identities.
CK-12 Foundation
Ck 12: Trigonometry: Trigonometry in Terms of Algebra
[Free Registration/Login may be required to access all resource tools.] Define trigonometric relationships with algebraic ratios.