For all real numbers x, cos(2x)=?

3 Answers

• This is also known as the double angle trig identity which is cos2x=cos^2x-sin^2x

• cos(2x) = cos²x – sin²x

  sin²x + cos² x = 1

  sin²x = 1 – cos²x

  cos(2x) = 1 – cos²x + cos²x

  cos(2x) = 1

  x = 0

• 3x times 4

• cos^2(x) – sin^2(x)

  It’s called a trigonometric identity.

• cos (2x) = cos²x – sin²x = 1 – 2sin²x = 2cos²x – 1