原式=-(m-3)/2(m-2)÷[(m+2)(m-2)-5]/(m-2)
=-(m-3)/2(m-2)÷(m²-9)/(m-2)
=-(m-3)/2(m-2)×(m-2)/(m+3)(m-3)
=-1/2(m+3)
=-1/(2m+6)