(1)=(y+3)²(3-y)²=(y²-9)²=y^4-18y²+81
(2)=(2a+b+1)(2a+b-1)=(2a+b)²-1=4a²+4ab+b²-1
(3)=(a-2b-3)(a+2b+3)=a²-(2b+3)²=a²-4b²-12b-9