Question

cos 2x is equal to cos squared 2x minus sin squared 2x ​

Answer 1

Answer:

It's, at the most basic level, because of the Pythagorean Theorem - In a right triangle, the sum of the squares of the sides (opposite and adjacent) equals the square of the hypotenuse (the side across from the right angle).

Answer 2

Answer:

It is an identity that

$\cos2 \alpha = { \cos }^{2} 2 \alpha - { \sin}^{2} 2 \alpha$