x1,x2是一元二次方程x²-4x＋1=0的两个实数根
∴x1+x2=4,x1x2=1
⒈（X1+X2）² =4²=16
⒉1/x1+1/x2
=(x1+x2)/x1x2
=4
⒊（x1－x2）²
=(x1+x2)²-4x1x2
=4²-4
=12