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[求助]
【求解】 一元四次方程
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| 求解一元四次方程 X^4-3X+1=0,想知道解題步驟,最后結(jié)果應(yīng)該為(1±√5)/2 |
或許以后有用 |
金蟲(chóng) (初入文壇)
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若ax^4+bx^3+cx^2+dx+e=0 令 D=-(3b^2-8ac) E=3b^4+16a^2c^2-16abc+16a^2bd-64a^3e F=-(b^3-4abc+8a^2d)^2 A=D^2-3E,B=DE-9F,C=E^2-3DF,Δ=B^2-4AC 1.若D=E=F=0,則方程有一個(gè)四重根。則 x1=x2=x3=x4=-b/4a=-2c/3b=-3c/2d=-4e/d 2.若A=B=C=0,且DEF不為0,則方程有一個(gè)三重根。則x1=-b/4a-F/4aD x2=x3=x4=-b/4a+3F/4aD 3.若E=F=0,D不為零,則方程有兩對(duì)重根。 x1=x2=(-b+(-D)^(1/2))/4a x3=x4=(-b-(-D)^(1/2))/4a 4.若Δ=0,A不為零,則方程只有一對(duì)重根。 令X1=-D+B/A,X2=-B/2A,則 x1=(-b+X1^(1/2)+2X2^(1/2))/4a x2=(-b+X1^(1/2)-2X2^(1/2))/4a x3=x4=(-b+X1^(1/2))/4a 5.若Δ<0,令T=arccos[(2AD-3B)/2A^(3/2)] y1=-(D+2A^(1/2)cos(T/3) y2=-(D+2A^(1/2)cos(T/3+2π/3) y3=-(D+2A^(1/2)cos(T/3-2π/3) x1=(-b+y1^(1/2)+y2^(1/2)+y3^(1/2))/4a x2=(-b+y1^(1/2)-y2^(1/2)-y3^(1/2))/4a x3=(-b-y1^(1/2)-y2^(1/2)+y3^(1/2))/4a x4=(-b-y1^(1/2)+y2^(1/2)-y3^(1/2))/4a 6.若Δ>0 Y1=AD+(3/2)(-B+(B^2-4AC)^(1/2)) Y2=AD+(3/2)(-B-(B^2-4AC)^(1/2)) Z1=(-2D-Y1^(1/3)-Y2^(1/3)/6 Z2=3^(1/2)(Y1^(1/3)-Y2^(1/3)/6 Z=-(D+Y1^(1/3)+Y2^(1/3)/3 W1=(2Z1+2(Z1^2+Z2^2)^(1/2))^(1/2) W2=(-2Z1+2(Z1^2+Z2^2)^(1/2))^(1/2) x1=(-b+Z^(1/2)+2W1)/4a x2=(-b+Z^(1/2)-2W1)/4a x3=(-b-Z^(1/2)-2W2)/4a x4=(-b-Z^(1/2)+2W2)/4a |

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