原式=(m-2)/[2(m+2)(m-2)]-m/[2m(m+3)]
=1/[2(m+2)]-1/[2(m+3)]
=(m+3)/[2(m+2)(m+3)]-(m+2)/[2(m+2)(m+3)]
=[(m+3)-(m+2)]/[2(m+2)(m+3)]
=1/[2(m+2)(m+3)]