已知tana=1/3,求sinacosa

Question

如题所述

Answer 1

已知tana=1/3,求sinacosa
解：
sinacosa
=sinacosa/(sin²a+cos²a)
=（tana）/(tan²a+1)
=(1/3)/[(1/3)²+1]
=(1/3)/(1/9+1)
=3/10本回答被提问者采纳

Answer 2

tan2a=2tana=2/3
sin2a=2/根号13
sinacosa=sin2a/2=1/根号13=根号13/13