已知x1 x2 是关于方程x²-6x+k=0的两个实数根,且x1²x2²-x1-x2=115.
求k的值,再求x1²+x2²+8的值
人气:433 ℃ 时间:2020-01-25 16:21:59
解答
解析原式:(x1x2)²-(x1+x2)=115根据韦达定理x1x2=c/a=kx1+x2=-b/a=6所以:(x1x2)²-(x1+x2)=115k²-6=115k=11或-11(2)x1²+x2²=(x1+x2)²-2x1x2+8=36-2k=36-22+8=14+8=22或36+22+8=66...能用初三的知识回答吗··有点看不懂是初三的韦达定理x1+x2=-b/ax1x2=c/a这是公式ax²+bx+c=0x²前面的是ax前面的是b,常数是c比较
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