tan(a/2)=(sina)/(1＋cosa)
sin22.5°/sin67.5°
=sin22.5°/cos22.5°
=tan22.5°
=(sin45°)/(1＋cos45°)
=[√2/2]/[1＋(√2/2)]
=√2－1
tan22.5=30/X=√2－1
X=30/(√2－1 ) 高
cos67.5=30/y
cos67.5=cos135/2
cos135=-√2/2=2(cos67.5)^2-1
(cos67.5)^2=(1-√2/2)/2=(2-√2)/4
cos67.5>0
所以cos67.5=[√(2-√2)]/2
[√(2-√2)]/2=30/y
y=60/[√(2-√2)] 腰