把x=α代入方程x²+3x-2=0,可得:
α²+3α-2=0
α²+2α+α-2=0
α²+2α=2-α
根据韦达定理,可得:α+β=-3
α²+2α-β=2-α-β
=2-(α+β)
=2-(-3)
=2+3
=5