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  • sin10°*sin50°*sin70°等于好多

    sin10°*sin50°*sin70°等于好多
    數(shù)學(xué)人氣:491 ℃時(shí)間:2020-02-05 15:36:03
    優(yōu)質(zhì)解答
    sin10°×sin50°×sin70°= sin10°×sin50°×sin70°× cos10°/cos10°= sin10°× cos10°×sin50°×sin70°/cos10°= (1/2) × sin20°× sin50°× sin70°/cos10°= (1/2) × sin20°× sin50°× cos20°/...= (1/2) × sin20°× sin50°× sin70°/cos10°
    = (1/2) × sin20°× sin50°× cos20°/cos10°
    = (1/4) × sin40°× sin50°/cos10°
    = (1/4) × sin40°× cos40°/cos10°
    = (1/8) × sin80°/cos10°
    = (1/8) × sin80°/sin80°
    = 1/8為什么sin10°×sin50°×sin70°
    =sin10°cos10°×cos20°×cos40°/cos10°
    =1/2 sin20°×cos20°×cos40°/cos10°
    =1/4 sin40°×cos40°/cos10°
    =1/8 sin80°/cos10°
    =1/8
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