[a²-2×a×2b+(2b)²]/[a²-(2b)²]
=(a-2b)^2/(a+2b)(a-2b)
=(a-2b)/(a+2b)[a²-2×a×2b+(2b)²]/[a²-(2b)²]请一步一步写出，谢谢[a²-2×a×2b+(2b)²]=a^2-4ab+4b^2=(a-2b)^2[a²-(2b)²]=a^2-4b^2=(a+2b)(a-2b)