cos^4 30 - sin^4 30
Assuming degrees we have
cos^4 (30) - (sin^4 30) factor
[ oos^2 ( 30) + sin^2 (30) ] [ cos^2 (30) - sin^2 (30) ]
[ 1 ] [ (√3 / 2 ) ^2 - ( 1 / 2) ^2 ]
3 / 4 - 1 / 4
2 / 4 = 1 / 2