sinθ cosθ tanθ

用x代表θ:
90> x >45
tan x肯定 > 1
sin x肯定≦1
cos x肯定<1
所以(1)同(2)係岩

sin x< cos x
sin x/cos x < 1
tan x<1
上邊都講過 90> x >45
tan x 肯定 > 1:
所以(3)係錯:
Ans:1&2

1. tanθ > sinθ
1/cosθ > 1
cosθ < 1
0˚<θ<90˚
So 1 must be true

2. tanθ > cos θ
sinθ > (cosθ)^2
sinθ > 1-(sinθ)^2
(sinθ)^2 + sinθ -1 > 0
-1<sinθ<0.618
38.1˚<θ<90˚
So 2 must be true

3. cosθ > sinθ
sinθ/cosθ < 1
tanθ < 1
As 45˚ <θ< 90˚, no solution for tanθ < 1
So 3 must not be true

Assume that θ=60˚.

tan60=1/root3,sin60=root3/2,tan60<sin60.
cos60=0.5,tan60>cos60.
cos60<sin60.

So 2. is the most probable true result.