$\frac{-3}{9}xy$  

 $\frac{6}{9}xy$  

 $\frac{-2}{3}xy$  

none

a²-b²

a²-4b⁴

a²+b²

a²-4b²

(x+1) and (x+2y)

(x+y) and (x+2y)

(x+y) and (x-2y)

(x-y) and (x+2y)

5xy+15xy

20y+15xy

5x²+4xy

20x+15x²y