help! 1.Если cosa=-0.5, то 3sin^2a-cos^2a=

Question

help!

1.Если cosa=-0.5, то 3sin^2a-cos^2a=

Answer 1

 cosa=-0.5    sin^2a=1-cos^2a=1-0.25=0.75

3sin^2a-cos^2a=3*0.75-0.25=2