sin1*sin2*...*sin89
http://latex.codecogs.com/gif.latex?\dpi{300}&space;\fn_cs&space;\sin&space;1^{\circ}\times&space;\sin&space;2^{\circ}\times&space;\sin&space;3^{\circ}\times&space;...\times&space;\sin&space;89^{\circ}=?????? 2# zwh2010:b:
有才! $sin(a)^2={1-cos(2a)}/2$
设$z=exp(2ia)$
那么$(1-z)(1-\bar{z})=2(1-cos(2a))$
然后易得
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