求cos[(pai)/9]*cos[(2pai)/9]*cos[(3pai)/9]*cos[(4pai)/9]的值要求有过程.细致点.

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求cos[(pai)/9]*cos[(2pai)/9]*cos[(3pai)/9]*cos[(4pai)/9]的值要求有过程.细致点.
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求cos[(pai)/9]*cos[(2pai)/9]*cos[(3pai)/9]*cos[(4pai)/9]的值要求有过程.细致点.
求cos[(pai)/9]*cos[(2pai)/9]*cos[(3pai)/9]*cos[(4pai)/9]的值
要求有过程.
细致点.

求cos[(pai)/9]*cos[(2pai)/9]*cos[(3pai)/9]*cos[(4pai)/9]的值要求有过程.细致点.
[sin(π/9)*cos(π/9)cos(2π/9)cos(3π/9)cos(4π/9)]/sin(π/9)
=[1/2*sin(π/9)*cos(π/9)cos(2π/9)cos(4π/9)]/sin(π/9)
={1/2*[1/2*sin(2π/9)cos(2π/9)cos(4π/9)]}/sin(π/9)
={1/4*[1/2*sin(4π/9)cos(4π/9)]}/sin(π/9)
={1/8*[1/2*sin(8π/9)]}/sin(π/9)
=1/16*[sin(8π/9)/sin(π/9)]
=1/16*[sin(π/9)/sin(π/9)]
=1/16