A rectangular game board is composed of identical squares arranged in a
rectangular array of "r" rows and "r+1" columns. The "r" rows are numbered
from "1" through "r", and the "r+1" columns are numbered from "1" through
"r+1". If "r">10, which of the following represents the number of squares
on the board that are neither in the 4th row nor in the 7th column?
选项有
r^2-r r^2-1 r^2 r^2+1 r^2+r
抱歉平方只能这样打
正确答案是
r^2-r
请问有人知道为什么吗
谢谢!