=sina+2sinacosa+sin(a+2a)
=sina+2sinacosa+sinacos2a+sin2acosa
=sina+2sinacosa+sinacosacosa-sinasinasina+2sinacosacosa
=sina+2sinacosa+3sinacosacosa-sinasinasina
……
解不下去了……
忘了很多公式
sina+sin2a+sin3a最大值
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