(3a-b)(3a+b)+b^2 9x^2-(y+4x)(y-4x) (5c-6d)(5c+6d)-25c^2 (7m-10n)(7m+10n)-100n^2
(3a) ²-b²+b²=9a² 9x²-y²+16x²=25x²-y² 25c²-36d²-25c²=-36d² 49m²-100n²-100n²=49m²-200n²