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已知 Cos(π+α)=% 3 2 ,...

cos[π/2-(π/6+α)]=sin(π/6+α)=1/3 所以cos(π/3-α)=1/3 利用倍角公式 则cos2(π/3-α)=cos(2π/3-2α)=2[cos(π/3-α)]^2-1=2*(1/9)-1=-7/9

cos(3 π/4 +2α) =-cos[π-(3 π/4 +2α)] =-cos[ π/4 -2α] =-cos[2( π/8 -α)] =-2cos²[( π/8 -α)]+1 =

π

=-7/9

解:依题意知coa3π/2cosa-sin3π/2sina=3/5 联立sina^2+cosa^2=1得cosa=-4/5 即cos(a-π/3)=cosacosπ/3+sinasinπ/3=-2/5+3√3/10=3√3-4/10 很高兴为您解答,祝你学习进步>学习宝典】团队为您答题。 有不明白的可以追问!如果您认可我的回答。 请点...

cosa = -cos(兀+a) = 1/3,所以 sina = ±2√2/3, 则 tan(兀/2 - a) = cota = cosa / sina = ±√2/4 。

sin a=2/3,a属于(π/3,π),cosa

sin(2π+α)/tan(-α-π)cos(-a)tan(π+α)=sinα/tan(-α)cos(a)tanα=sinα/sin(-α)tanα=-1/tanα

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