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x-4-ax-3-bx-2-cx-d-0-




Question Number 198772 by ajfour last updated on 24/Oct/23
x^4 +ax^3 +bx^2 +cx+d=0
x4+ax3+bx2+cx+d=0
Commented by Frix last updated on 24/Oct/23
Usually we first try factors of d. The next  step would be substituting x=t−(a/4) to  reach t^4 +pt^2 +qt+r and now try to find  2 square factors (t^2 −ut−v)(t^2 +ut−w) by  matching the constants. This leads to  w^3 +αw^2 +βw+γ=0; if this has at least 1  useable solution an exact solution of the  given equation makes sense; otherwise it′s  better to approximate.
Usuallywefirsttryfactorsofd.Thenextstepwouldbesubstitutingx=ta4toreacht4+pt2+qt+randnowtrytofind2squarefactors(t2utv)(t2+utw)bymatchingtheconstants.Thisleadstow3+αw2+βw+γ=0;ifthishasatleast1useablesolutionanexactsolutionofthegivenequationmakessense;otherwiseitsbettertoapproximate.

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