若∠A为锐角,cos2A=½,则tanA等于多少?

若∠A为锐角,cos2A=½,则tanA等于多少?
若∠A为锐角,cos2A=½,则tanA等于多少?

若∠A为锐角,cos2A=½,则tanA等于多少?
cos2a=2cos²a-1=1/2
cos²a=3/4 cosa=√3/2
sin²a=1/4 sina=1/2
tana=√3/3

根号3/3
cos2A=1-2sin^2A=1/2
sin^2A=1/4
sinA=1/2
A=π/6
tanA=根号3/3

根号3