原式=[2sin^2x-(cos^2x-sin^2x)]/(cos^2x+sin^2x+cos^2x)
=(3sin^2x-cos^2x)/(sin^2x+2cos^2x)
=(3tan^2x-1)/(tan^2x+2)
=(3*2^2-1)/(2^2+2）
=11/6