A matrix A is said to be of rank r if there is at least one non zero minor of order r and every minor of order r+1 is zero.
Eg:
Consider a matrix A,
[2 -1 5]
|3 0 6|
[4 1 7]
|A|=0
So the minor of third order is zero
There exists a minor of second order
|3 0|
|1 4|
which is equal to 3
Thus a minor of second order is not zero.
So rank of A is 2
