已知x1 x2是方程x²+3x+1=0的两根：X1=(√5 - 3)/2,X2=(-√5-3)/2则：(X1)^2=(7-3√5)/2 (X2)^2=(7+3√5)/2 (X1)²-3(X2)²+20=3.5-1.5√5-3(3.5+1.5√5)+20=13-6√5