23. 小明和小华同解一个二元一次方程组$\left\{\begin{array}{l} ax+by= 16,\enclose{circle} {1}\\ bx+ay= 1,\enclose{circle} {2}\end{array}\right. $时,小明把方程①抄错,求得的解为$\left\{\begin{array}{l} x= -1,\\ y= 3;\end{array}\right. $小华把方程②抄错,求得的解为$\left\{\begin{array}{l} x= 3,\\ y= 2.\end{array}\right. $请你求出原方程组的解．

原方程组的解为$\begin{cases}x = -\frac{9}{7}\\y = \frac{26}{7}\end{cases}$

24. 若$\left\{\begin{array}{l} x= 2,\\ y= 1\end{array}\right. 是方程组\left\{\begin{array}{l} mx-ny= 1,\\ nx+my= 8\end{array}\right. $的解,试求$3m-5n$的值．

$-9$

25. $\left\{\begin{array}{l} \frac {x}{2}+\frac {y}{3}= 2,\\ 2x+3y= 28.\end{array}\right. $

$\begin{cases}x = -4\\y = 12\end{cases}$

26. $\left\{\begin{array}{l} \frac {x+y}{2}-\frac {y-x}{3}= 6,\\ 2(x+y)-(x-y)= -4.\end{array}\right. $

$\begin{cases}x = 8 \\ y = -4 \end{cases}$