• 7. Angle sum and difference identities
    These are also known as the  addition and subtraction theorems  or  formulae . The identities can be derived by combining right triangles ...
  • 4. Pythagorean identity
    In trigonometry, the basic relationship between the sine and the cosine is known as the Pythagorean identity: {\displaystyle \sin ^{2}\...
  • 6. Symmetry, shifts, and periodicity
    By examining the unit circle, the following properties of the trigonometric functions can be established. Symmetry When the trigon...