\(2x^4-21x^3+74x^2-105x+50=0\)
\(< =>2x^4-10x^3-11x^3+55x^2+19x^2-95x^2-10x+50=0\)
\(< =>2x^3\left(x-5\right)-11x^2\left(x-5\right)+19x\left(x-5\right)-10\left(x-5\right)=0\)
\(< =>\left(x-5\right).\left(2x^3-11x^2+19x-10\right)=0\)
\(< =>\left(x-5\right).\left(2x^3-2x^2-9x^2+9x+10x-10\right)=0\)
\(< =>\left(x-5\right).\left(x-1\right).\left(2x^2-9x+10\right)=0\)
\(2x^2-9x+10\ge0\)
\(< =>x=5\)hoặc \(x=1\)
Vậy S = 1 hoặc 5
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