求方程3x²+5y²=345的正整数解3x²=5(69-y²)设：x=5x'15x'²=69-y²y²=3(23-5x'²)设：y=3y'3y'²=23-5x'²5x'²+3y'²=23x'=2,y'=1x=10,y=3