用公式法
x={(3m-n)±√ ̄[(n-3m)^2-4×2×(-2m^2+3mn-n^2)]}/(2×2)
=[(3m-n)±√ ̄(25m^2-30mn+9n^2)]/4
=[(3m-n)±(5m-3n)]/4
x=2m-n或x=-1/2m+1/2n
用公式法
x={(3m-n)±√ ̄[(n-3m)^2-4×2×(-2m^2+3mn-n^2)]}/(2×2)
=[(3m-n)±√ ̄(25m^2-30mn+9n^2)]/4
=[(3m-n)±(5m-3n)]/4
x=2m-n或x=-1/2m+1/2n