PSAT 8/9 P1 · 第 21 题

PSAT 8/9 P1 · 原库模块 3 · Q21 原库参考解析

8x +7y =9
24x +21y =27
For each real number r, which of the following points lies on the graph of each equation in the xy-plane for the given system?

解题思路