4-【1/4(sin2α)平方】-【(sinα)平方】-【(cosα)四次方】=4-1/4*(2sinacosa)^2-【(sinα)平方】-【(cosα)四次方】=4-sin^2acos^2a-cos^4a-sin^2a=4-cos^2a(sin^2a+cos^2a)-sin^2a=4-cos^2a-sin^2a=4-(sin^2a+cos^...