Trigonometric Identities

I. Reciprocal Identities   II. Quotient Identities   III. Pythagorean Identities   IV. Cofunction Identities   V. Even/Odd Identities   VI. Sum and Difference Identities   VII. Double Angle Identities   VIII. Half Angle Identities   IX. Product-to-Sum Identities   X. Sum-to-Product Identities     XI. Other Trig Formulas Law of Sines         Law of Cosines         Area of Triangle