2x1x2+(x1+x2)+1=0 .(1) (x1+x2)^2-4x1x2-5/4=0.(2) 两式如何联立
1个回答

(1)×2+(2)得

(x1+x2)^2+2(x1+x2)+3/4=0

解为x1+x2=-1/2或x1+x2=-3/2

当x1+x2=-1/2时x1x2=-1/4,解为

(1)x1=(-1+√5)/4,x2=(-1-√5)/4

(2)x1=(-1-√5)/4,x2=(-1+√5)/4

当x1+x2=-3/2时x1x2=1/4,解为

(3)x1=(-3+√5)/4,x2=(-3-√5)/4

(4)x1=(-3-√5)/4,x2=(-3+√5)/4

方程组的解有四组为

(1)x1=(-1+√5)/4,x2=(-1-√5)/4,(2)x1=(-1-√5)/4,x2=(-1+√5)/4,(3)x1=(-3+√5)/4,x2=(-3-√5)/4,(4)x1=(-3-√5)/4,x2=(-3+√5)/4.