不是都有 $x_i$ 和 $y_i$ 的范围了吗/yiw
by diqiuyi @ 2024-04-18 18:58:53
啊是 $\sum x_i$
by diqiuyi @ 2024-04-18 18:59:21
袜，事晓易隆！
by whhsteven @ 2024-04-18 19:08:21