作业帮(3)sin29π/9cos4π/9+sin41π/18cos19π/18
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(3)sin29π/9cos4π/9+sin41π/18cos19π/18
(3)sin29π/9cos4π/9+sin41π/18cos19π/18
(3)sin29π/9cos4π/9+sin41π/18cos19π/18
原式 = sin(3π +2π/9) cos(4π/9) + sin(2π + 5π/18) cos(π + π/18)
= - sin(2π/9) cos(4π/9) + sin(5π/18) cos(π/18)
= - 1/2 [ sin(2π/9 + 4π/9) + sin(2π/9 - 4π/9) ] + 1/2 [ sin(5π/18+π/18) - sin(5π/18 - π/18) ]
（积化和差）
= - 1/2 [ sin(2π/3) - sin(2π/9) ] + 1/2 [ sin(π/3) - sin(2π/9) ]
= -1/2 sin(2π/3) + 1/2 sin(π/3)
= 0
(3)sin29π/9cos4π/9+sin41π/18cos19π/18
(3)sin29π/9cos4π/9+sin41π/18cos19π/18
求值：sin29π|9cos4π|9+sin41π|18cos19π|18哥哥,姐姐们帮帮小弟……
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