先化简,再求值：m-3/3m²-6m÷(m+2-5/m-2）,其中m是方程x²+3x-1=0的根

x=m
所以m²+3m-1=0
m²+3m=1
原式=(m-3)/3m(m-2)÷(m²-4-5)/(m-2)
=(m-3)/3m(m-2)×(m-2)/(m+3)(m-3)
=1/3m(m+3)
=1/3(m²+3m)
=1/3