Question

若a为锐角,且满足SINa=3COSa,则SINa*COSa的值

Answer 1

(sina)^2+(cosa)^2=1,

(3cosa)^2+(cosa)^2=1,

10(cosa)^2=1,

(cosa)^2=1/10,

sina*cosa

=3cosa*cosa

=3(cosa)^2

=3/10,