问题 填空题
已知实数a,b,c满足abc=-1,a+b+c=4,
a
a2-3a-1
+
b
b2-3b-1
+
c
c2-3c-1
=
4
9
,则a2+b2+c2=______.
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)

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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