✔ 最佳答案
cos2x = 1 - 2 sin^2 x
cos45∘ = 1 - 2 sin^2 22.5∘
1/sqrt(2) = 1 - 2 sin^2 22.5∘
sin^2 22.5∘= 1/2 ( 1 - 1/sqrt(2) )
sin 22.5∘= sqrt[ 1/2 ( 1 - 1/sqrt(2) ) ]
2007-06-08 20:48:06 補充:
做少左, 補返比你csc^2 22.5∘= 2sqrt(2) / ( sqrt(2) - 1)= 2sqrt(2)( sqrt(2) + 1) / 1= 4 + 2sqrt(2)