Question

方程x平方+5x-1=0的两个根是x1,x2,则x1平方+x2平方等于多少

Answer 1

x1+x2=-5;

x1*x2=-1;

x1^2+x2^2=(x1+x2)^2-2x1*x2=(-5)^2-2(-1)=27