解二元一次方程 (19 20:53:55)
{3x+2y=20      （括号是连一块的）
{4x-5y=19         
                                                                                                                                                                                                                 
第二题：已知方程组{5x+y=3,                            
                           {ax+5y=4  
            与方程组  {x-2y=5
                            {5x+by=1       有相同的解,求a、b的值