Question 152655
Where are you looking if the indices i and j are equal in a square matrix?
a. Along the middle row
b. Along the middle column
c. Along the diagonal from the upper left to the lower right
d. Along the diagonal from the lower left to the upper right
0 solutions
<pre><font size = 4 color = "indigo"><b>
Notice in the matrix:

{{{(matrix(4,4,a[1,1],a[1,2],a[1,3],a[1,4],a[2,1],a[2,2],a[2,3],a[2,4],a[3,1],a[3,2],a[3,3],a[3,4],a[4,1],a[4,2],a[4,3],a[4,4]))}}}

the way the elements have subscripts, for instance,
{{{a[i,j]=a[3,2]}}} means the element where {{{i=3}}} 
and {{{j=2}}}.

The first subscript, which is denoted by {{{i}}}, is
the number of the row it's in and the second subscript,
which is denoted by {{{j}}} is the number of the column 
that it's in.

{{{(matrix(4,4,a[1,1],a[1,2],a[1,3],a[1,4],a[2,1],a[2,2],a[2,3],a[2,4],a[3,1],a[3,2],a[3,3],a[3,4],a[4,1],a[4,2],a[4,3],a[4,4]))}}}

So picking out the elements where i and j are equal,
they are 
{{{ a[1,1] }}}, {{{ a[2,2] }}}, {{{ a[3,3] }}}, and {{{ a[4,4] }}}   

Notice they appear on the diagonal that goes from the upper
left corner to the bottom right corner.

So the answer is (c).

Edwin</pre>