sec is the abbreviation for second
tan is what one may get while visiting the beach
sin is a transgression
cos is the nickname of a famous black comedian
... in other words, a trig function without an argument means nothing.
now, if you meant ...
... then I recommend multiplying the left side of the equation by , then using the Pythagorean identity
now, can you be more clear with this equation ...
how would you verify 8sin^2cos^2=1-cos4?