ãåèçæ¡ã
11ã0
âµf(n)=sin(30n)°
â´åå¼=sin30°+sin90°+sin150°+sin210°+sin270°+sin330°=0
12ã17/9
åå¼=(1/2)- (1/2)Ã(-1)-(1/3)Ã(1/3)-(-1)+(-â3/2)+(â3/2)
=(1/2)+(1/2)-(1/9)+1
=2-(1/9)
=17/9
13ãf(x)=sin2x-cosx
âµf(x)æ¯å¥å½æ°ä¸x>0æ¶ï¼f(x)=sin2x+cosx
â´f(-x)=-f(x)=-sin2x-cosx=sin(-2x)-cos(-x)
â´x<0æ¶ï¼f(x)=sin2x-cosx
14ã-â3/2
(cosa-sina)²=1-2sinacosa=1-2Ã(1/8)=3/4
âµ Ï/4<a<Ï/2
â´ cosa<sina
â´cosa-sina=-â(cosa-sina)²=-â(3/4)=-â3/2
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