x1x2是方程2x²一3x一3＝0的两个实数根则x1/x2十x2/x1的值为

题目

x1x2是方程2x²一3x一3＝0的两个实数根则x1/x2十x2/x1的值为

答案

x1+x2=3/2,
x1x2=-3/2
x1/x2+x2/x1=(x1²+x2²)/(x1x2)=[(x1+x2)²-2x1x2]/(x1x2)=(x1+x2)²/(x1x2)-2=(9/4)/(-3/2)-2=-3/2-2=-7/2