(m-2)/(4㎡-4m)=(m-2)/[4m(m-1)](m-1)/(㎡-2m)= (m-1)/[m(m-2)] 最小公分母:4m(m-1)(m-2)(m-2)/(4㎡-4m)=(m-2)²/[4m(m-1)(m-2)](m-1)/(㎡-2m)= 4(m-1)²/[4m(m-1)(m-2)]