4m²-4m+1/m+1 ÷ 4m²-1/m²-1
=(2m-1)²/(m+1)×m²-1/4m²-1
=(2m-1)²/(m+1)×(m+1)(m-1)/(2m+1)(2m-1)
=(2m-1)(m-1)/(2m+1)