Question

谁来帮我解两道一元二次方程的问题

Answer 1

题目有误；不是X12+8X2+20=,而是 X1^3+8X2+20=

1.X1、X2是方程X^2+3X+1=0的两实数根

由韦达定理得:

X1+X2=-3 X1X2=1

x1^3+8x2+20

=-x1*(3x1+1)+8x2+20

=-3x1^2-x1+8x2+20

=-3*(x1^2)-x1+8x2+20

=3*(3x1+1)-x1+8x2+20

=8(x1+x2)+23

=-24+23

=-1

2.根据题意可得x1+x2=- =-4,x1•x2= =-3,

又∵2x1(x2^2+5x2-3）+a=2,

∴2x1x2^2+10x1*x2-6x1+a=2,

-6x2+10x1*x2-6x1+a=2,

-6（x1+x2）+10x1x2+a=2,

-6×（-4）+10×（-3）+a=2,

∴a=8．