Question

不解方程,求一元二次方程2x平方+3x-1=0的两个根的1.平方和2.倒数和

Answer 1

2x平方+3x-1=0

根据韦达定理

x1+x2=-b/a=-3/2

x1*x2=c/a=-1/2

1.

平方和

x1^2+x2^2

=(x1+x2)^2-2x1x2

=(-3/2)^2-2*(-1/2)

=13/4

2.

倒数和

1/x1+1/x2

=(x1+x2)/x1x2

=(-3/2)/(-1/2)

=3