Đáp án:

MTC: 6(x+y)²

Quy đồng:

$\frac{1}{3x+3y}$ =$\frac{1.2(x+y)}{3(x+y).2(x+y)}$ =$\frac{2(x+y)}{6(x+y)^{2}}$

$\frac{1}{2x+2y}$ =$\frac{1.3(x+y)}{2(x+y).3(x+y)}$ =$\frac{3(x+y)}{6(x+y)^{2}}$

$\frac{1}{x^{2}+2xy+y^{2}}$ =$\frac{1.6}{(x+y)^{2}.6}$ =$\frac{6}{6(x+y)^{2}}$