解：a³-2a²-a+7=5
a³-2a²-a+2=0
(a³-2a²)-(a-2)=0
a²(a-2)-(a-2)=0
(a-2)(a²-1)=0
(a-2)(a+1)(a-1)=0
a-2=0或a+1=0或a-1=0
a=2或a=-1或a=1
a^3-2a^2-a+7=5即
a^3-2a^2-a+2=0
而a^3-2a^2-a+2
=(a^3-a^2)-(a^2+a-2)
=a^2(a-1)-(a+2)(a-1)
=(a-1)(a^2-a-2)
=(a-1)(a-2)(a+1)
=0解得
a=1或-1或2.
a^3-2a^2-a+7=5 a^3-2a^2-a+2=0 (a^3-a)+(-2a^2+2)=0 a(a^2-1)-2(a^2-1)=0 (a^2-1)(a-2)=0
(a-1)(a+1)(a-2)=0 所以a=1 or a=-1 or a=2
a^3-2a^2-a+7=5
a^3-2a^2-a+2=0
a^2(a-2)-(a-2)=0
(a^2-1)(a-2)=0
(a+1)(a-1)(a-2)=0
a1=-1 a2=1 a3=2
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