如何解方程a^4-7a^3+5a^2+7a-6?

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如何解方程a^4-7a^3+5a^2+7a-6?
如何解方程a^4-7a^3+5a^2+7a-6?

如何解方程a^4-7a^3+5a^2+7a-6?
a^4-7a^3+5a^2+7a-6=0
→(a^4-2a^3+a^2)-(5a^3-10a^2+5a)-(6a^2-12a+6)=0
→a^2(a^2-2a+1)-5a(a^2-2a+1)-6(a^2-2a+1)=0
→(a^2-2a+1)(a^2-5a-6)=0
→(a-1)²(a+1)(a-6)=0
∴a1=a2=1,a3=-1,a4=6.

f(a)=a^4-7a^3+5a^2+7a-6
f(1)=0
f(-1)=0
f(a) = (a-1)(a+1)(a^2+k1a +6)
coef. of a
-k1= 7
k1=-7
f(a) = (a-1)(a+1)(a^2-7a +6)
=(a-1)^2.(a+1)(a-6)