Question

Question #8c8ad

Answer 1

This can not be proven because it is not true.

Explanation:

It seems the only way to prevent questions like this from being re-posted is to write an answer (comments are ignored).

Assuming you are using the Spanish form (`sen`) for `sin`
then the given "equation" is invalid as can be demonstrated by a simple substitution of `(0)` for `a`

`cos^2(0) - 3sin^2(0) = 1-0 = 1 !=0`