(a^2-4b^2)/(a^2+2ab+b^2)÷(a+2b)/(a^2+ab)
=(a-2b)(a+2b)/(a+b)²xa(a+b)/(a+2b)
=a(a-2b)/(a+b)
=(a²-2ab)/(a+b)
不懂的欢迎追问.