方程组$\left\{\begin{array}{l}2x-3y=1,\\ 2x+5y=-2\\\end{array}\right.$中$x$的系数的特点是_____，方程组$\left\{\begin{array}{l}5x+4y=8,\\ 7x-4y=6\\\end{array}\right.$中$y$的系数的特点是_________，这两个方程组用_________消元法解较简便．