已知实数a,b,c满足abc=-1,a+b+c=4, a a 2 -3a-1 + b b 2 -3b-1 + c

2025-03-24 13:44:23
推荐回答(1个)
回答1:

∵abc=-1,a+b+c=4,
∴a 2 -3a-1=a 2 -3a+abc=a(bc+a-3)=a(bc-b-c+1)=a(b-1)(c-1),
a
a 2 -3a-1
=
1
(b-1)(c-1)

同理可得:
b
b 2 -3b-1 
=
1
(a-1)(c-1)
c
c 2 -3c-1
=
1
(a-1)(b-1)

a
a 2 -3a-1
+
b
b 2 -3b-1 
+
c
c 2 -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a 2 +b 2 +c 2 =(a+b+c) 2 -2(ab+bc+ac)=
33
2

故答案为:
33
2