问题
填空题
已知实数a,b,c满足abc=-1,a+b+c=4,
|
答案
∵abc=-1,a+b+c=4,
∴a2-3a-1=a2-3a+abc=a(bc+a-3)=a(bc-b-c+1)=a(b-1)(c-1),
∴
=a a2-3a-1
,1 (b-1)(c-1)
同理可得:
=b b2-3b-1
,1 (a-1)(c-1)
=c c2-3c-1
,1 (a-1)(b-1)
又
+a a2-3a-1
+b b2-3b-1
=c c2-3c-1
,4 9
∴
+1 (b-1)(c-1)
+1 (a-1)(c-1)
=1 (a-1)(b-1)
,4 9
∴
=(a-1)+(b-1)+(c-1) (a-1)(b-1)(c-1)
,即4 9
(a-1)(b-1)(c-1)=(a-1)+(b-1)+(c-1),4 9
整理得:
(abc-ab-ac-bc+a+b+c-1)=a+b+c-3,4 9
将abc=-1,a+b+c=4代入得:ab+bc+ac=-
,1 4
则a2+b2+c2=(a+b+c)2-2(ab+bc+ac)=
.33 2
故答案为:
.33 2