1、原式=(x+2y)/(x+y)*xy/(x+2y)÷(x+y)/xy=xy/(x+y)*xy/(x+y)=x²y²/(x+y)²
2、原式=(a+b)²/a²b²÷(b²-a²)/a²b²=(a+b)²/a²b²*a²b²/(a+b)(b-a)=(a+b)/(b-a)
3、原式=9x^4/16y²×2y/3x+x²/2y²×x/2y²=3x³/8y+x³/4y^4
4、原式=(a+b)²/(a-b)²×2(a-b)/3(a+b)-a²/(a+b)(a-b)×b/a=2(a+b)/3(a-b)-ab/(a+b)(a-b)
=(2a²+4ab+2b²-3ab)/3(a+b)(a-b)=(2a²+ab+b²)/(3a²-3b²)