(m+1)²/(2m+2)÷1/(m+1)×(m+3)(m-3)/(m+3)²
=(m+1)/2×(m+1)×(m-3)/(m+3)
=(m+1)²(m-3)/[2(m+3)]2m+2分之(m+1)²×m+1分之1×(m+3)² 分之(m+3)(m-3)(m+1)²/(2m+2)×1/(m+1)×(m+3)(m-3)/(m+3)²=1/2×(m-3)/(m+3)=1/2×[1-6/(m+3)]=1/2-3/(m+3)1/2怎么得出的？(m+1)²/(2m+2)×1/(m+1)=(m+1)²/[2(m+1)×(m+1)]=1/2