tanx=2平方得sin²x=4cos^2x5cos^2x=1 cos^2x=1/5sin^2x=4/5sinxcosx=√[sin^2xcos^2x]=2/5(2/3)sin^2x+(1/4)cos^2x=(8/12)sin^2x+(3/12)cos^2x=(3/12)[sin^2x+cos^2x]+(5/12)sin^2x=(3/12)+(5/12)sin^2x=3/12+(...