已知tana=2,求2/3sin^2a+1/4cos^2a的值!请高手作出详细过程!
热心网友
因为由公式 cos^2a=1/1+tan^2a 可得cos^2a=1/5原式=cos^2a(2/3tan^2a+1/4) =1/5(8/3+1/4) =7/12
热心网友
cos2a=1-tan^a/1+tan^a=-3/5sina2a=4/5代入原式=31/60
已知tana=2,求2/3sin^2a+1/4cos^2a的值!请高手作出详细过程!
因为由公式 cos^2a=1/1+tan^2a 可得cos^2a=1/5原式=cos^2a(2/3tan^2a+1/4) =1/5(8/3+1/4) =7/12
cos2a=1-tan^a/1+tan^a=-3/5sina2a=4/5代入原式=31/60