一元三次方程的韦达定理记忆技巧(一元三次方程的韦达定理)

导读 ax^3+bx^2+cx+d =a(x-x1)(x-x2)(x-x3) =a[x^3-(x1+x2+x3)x^2+(x1x2+x2x3+x1x3)x-x1x2x3] 对比系数得 -a(x1+x2+x3)=b a(x1x2+x2x3+x1...

ax^3+bx^2+cx+d =a(x-x1)(x-x2)(x-x3) =a[x^3-(x1+x2+x3)x^2+(x1x2+x2x3+x1x3)x-x1x2x3] 对比系数得 -a(x1+x2+x3)=b a(x1x2+x2x3+x1x3)=c a(-x1x2x3)=d 即得 x1+x2+x3=-b/a x1x2+x2x3+x1x3=c/a x1x2x3=-d/a。

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