(m-3)/(m平方-1)÷(m平方-3m)/(m平方+2m+1)-1/(m-1)
=(m-3)/(m-1)(m+1)×(m+1)²/m(m-3)-1/(m-1)
=(m+1)/m(m-1)-m/m(m-1)
=1/(m²-m)