a²+b²=25a+b=7(a+b)²=a²+b²+2ab=25+2ab=492ab=24ab=12(a-b)²=a²+b²-2ab=25-24=1a-b=±1∵a-b=±1,a+b=7∴a=3,b=4或者a=4,b=3∴a²-b²=9-16=-7或者16-9=7a²-b²