x²－4x＋2＝0
由韦达定理得：x1＋x2＝4,x1·x2＝2
∴(1) x1+x2+3x1x2=4+3*2=10
(2)x2/x1+x1/x2=(x2²+x1²)/x1x2=[(x1+x2)²-2x1x2]/x1x2=[16-4]/2=6