已知a2-3a-1=0,则代数式a3-10a的值是______

已知a2-3a-1=0,则代数式a3-10a的值是______.
2024-11-07 02:36:28
推荐回答(2个)
回答1:

法一:∵a2-3a-1=0,
(a? 

3
2
2
13
4
=0,
∴a-
3
2
13
2

∴a=
3± 
13
2

当a=
3+ 
13
2
时,a3-10a=
3+ 
13
2
×
13
?9
2
=3
当a=
3? 
13
2
时,a3-10a=
3? 
13
2
×
?3 
13
?9
2
=3;
法二:∵a2-3a-1=0,∴a2-1=3a,a2-3a=1,
则a3-10a=a3-9a-a=a3-3(a2-1)-a
=a3-3a2+3-a=a(a2-3a)+3-a=a+3-a=3.
故答案为:3

回答2:

a3-10a=a3-3a2+3a2-9a-a=a+3-a=3