已知tan=-1/3,求3sin^2+2sinacosa-cos^2a的值

问题描述:

已知tan=-1/3,求3sin^2+2sinacosa-cos^2a的值

3sin^2a+2sinacosa-cos^2a
=(3sin^2a+2sinacosa-cos^2a)/1
=(3sin^2a+2sinacosa-cos^2a)/(sin^2a+cos^2a)
=(3tan^2a+2tana-1)/(1+tan^2a)
=(1/3-2/3-1)/(1+1/9)
=-6/5