a rectangular game board is composed of identical squares arranged in a rectangular array of r rows

题目

a rectangular game board is composed of identical squares arranged in a rectangular array of r rows
a:r^2-r
b:r^2-1
c:r^2
d：r^2+1
e:r^2+r
a rectangular game board is composed of identical squares arranged in a rectangular array of r rows and r+1columns.the r rows are numbered from 1 through r,and the r+1 columns are numbered from r through r+1，if 人》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

答案

本题选a!
就是r*(r+1)格中去掉第4行第7列的格子后还有几格,
所以
共有:r*(r+1)-(r+r+1)+1
=r^2+r-2r-1+1=r^2-r.