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问题: 高一数学题

求sina=sin(a+2pai/3)+sin(a-2pai/3)

解答:

求sina=sin(a+2π/3)+sin(a-2π/3)
解:
sina=sin(a+2π/3)+sin(a-2π/3)
sina=2sinacos(2π/3)
sina=-(√3)sina
(1+√3)sina=0
sina=0
a=kπ , k∈Z