5a+7b
7p-2q
ax-by
x3+xy
11a-12b
6x2y-5xy2
-x-y
-xyz-abc
a2x3-b2y4
108
606
a-b+c
ax+b+2
xy+yz-zx
3p+2q-5r
x2-y2-z2
7a2+8b2-5c2
(x+y)2+2(x+y)(x-y)+(x-y)2
(2a+3b)2-2(2a+3b)(3b-a)+(3b-a)2