X²+XY=12 XY+Y²=13
1.（X+Y）²=X²+XY+XY+Y²=25 (X-Y)(X+Y)=-1 (X-Y)²=1/(X+Y)²=1/25
2.X²+Y²=[（X+Y）²+（X-Y）²]/2=(25+1/25)/2=12.52
3.X4+Y4=[（X²+Y²）²+（X²-Y²）²]/2=(12.52²+1/25²)=计算器吧