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sin10sin30sin50sin70=多少 急呀!!!!!

由sin(90-α)=cosα 和 2sinαcosα=sin2α 得: sin10sin30sin50sin70 =cos80cos60cos40cos20 =cos80*1/2*cos40(cos20sin20)/sin20 =1/2*cos80cos40*1/2*sin40/sin20 =1/4*cos80*(cos40sin40)/sin20 =1/4*cos80*1/2*sin80/sin20 =1/8*cos80sin80/sin...

sin10=cos(90-10)=cos80 sin30=cos(90-30)=cos60 对于小于90度的角a sina=cos(90-a)

13“sin10sin30sin50sin70”你这串是什么东西

sin10°sin50°sin70° =sin10°*1/2(cos20°-cos120°) =1/2sin10°(cos20°+1/2) =1/4(sin30°-sin10°)+1/4sin10° =1/4sin30° =1/8 ∴sin10°sin30°sin50°sin70° =1/2*1/8 =1/16

sin10*sin30*sin50*sin70 =cos10*sin10*sin30*sin50*sin70/cos10 =1/2*sin20*sin70*sin30*sin50/cos10 =1/2*sin20*cos20*sin30*sin50/cos10 =1/4sin40*sin50*sin30/cos10 =1/4sin40*cos40*sin30/cos10 =1/8sin80*sin30/cos10 =1/8cos10*sin30/co...

1.解sin10*sin30*sin50*sin70 =cos10*sin10*sin30*sin50*sin70/cos10 =1/2*sin20*sin70*sin30*sin50/cos10 =1/2*sin20*cos20*sin30*sin50/cos10 =1/4sin40*sin50*sin30/cos10 =1/4sin40*cos40*sin30/cos10 =1/8sin80*sin30/cos10 =1/8cos10*sin3...

分子 分母 同时乘以 cos10° sin10°×sin50°×sin70° = sin10°×sin50°×sin70°× cos10°/cos10° = sin10°× cos10°×sin50°×sin70°/cos10° = (1/2) × sin20°× sin50°× sin70°/cos10° = (1/2) × sin20°× sin50°× cos20°/cos10° = (1/4) × sin40°× sin50°...

10=90-80

答案为;1/2, 4sin10sin50sin70 =4cos80cos40cos20 =4cos80cos40cos20sin20/sin20 =2cos80cos40sin40/sin20 =sin80cos80/sin20 =2sin80cos80/2sin20 =sin160/2sin20 =1/2 其实不止这一种方法,还有很多种,记得给我加分啊,谢谢啊1

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