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设a=2[cos(2pai/17)+cos(4pai/17)+cos(8pai/17)+cos(16pai/17)]>0
a1=2[cos(6pai/17)+cos(10pai/17)+cos(12pai/17)+cos(14pai/17)]<0
åæa+a1=-1,a*a1=-4,å³a,a1æ¯æ¹ç¨x^2+x-4=0çæ ¹ï¼æ以é¿ä¸º|a|å|a1|ç线段å¯ä»¥ååºã
令b=2[cos(2pai/17)+cos(8pai/17)]>0 b1=2[cos(4pai/17)+cos(16pai/17)]<0
c=2[cos(6pai/17)+cos(10pai/17)]>0 c1=2[cos(12pai/17)+cos(14pai/17)]<0
åæb+b1=a b*b1=-1 c+c1=a1 c*c1=-1
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åæ2cos(2pai/17)+2cos(8pai/17)ï¼b [2cos(2pai/17)]*[2cos(8pai/17)]=c
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