The sine double angle formula involves trigonometric functions of double angles, i.e sin2A.

The cosine double angle formula involves trigonometric functions of double angles, i.e cos2A.

The tangent double angle formula involves trigonometric functions of double angles, i.e tan2A.

The sum of two trigonometric functions can be expressed as a single trigonometric function in the form Rcos(x±α) or Rsin(x±α).