已知实数a,b,c满足abc=-1,a+b+c=4,aa

问题描述:

已知实数a,b,c满足abc=-1,a+b+c=4,
a
a
1个回答 分类:数学 2014-12-09

问题解答:

我来补答
∵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),

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)=
4
9,即
4
9(a-1)(b-1)(c-1)=(a-1)+(b-1)+(c-1),
整理得:
4
9(abc-ab-ac-bc+a+b+c-1)=a+b+c-3,
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.
 
 
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