(2a-3)(2a+3)=4a^2+6a-6a-9=4a^2-9
(a-2)(a+2)=a^2+2a-2a-4=a^2-4
(a-3d)^2(3b+4)^2=(a^2-6ad+9d^2)(9b^2+24b+16)=9a^2b^2+24ba^2+16a^2-54adb^2-144adb-96ad+81d^2B^2+216bd^2+144D^2
(5a-2)^2(a+4c)^2=(25a^2-20a+4)(a^2+8ac+16c^2)=25a^4+200a^3c+400c^2-20a^3-160a^2c-320ac^2+4a^2+32ac+64c^2