⑴b(b+c)+c(b+c)
⑵3x2(a-b)-x(b-a)
⑶9x2- y2
⑷49(a-b)2-16(a+b)2
⑸x2y2-8xy+16
⑹a2-2a(b+c)+(b+c)2
⑺x2y-y
⑻3ax2+6axy+3ay2
⑼81m4-1
⑽a4-8a2b2+16b4