Rank of a matrix being 1 denotes that number of non-zero rows in Echleon form is 1. So in that case, after converting the given matrix to echleon form whereby you will get 2 rows or 2 columns of the transformed matrix as 0, you need to equate whatever element you get regarding x to zero so that the above mentioned condition is satisfied( i.e. getting two rows or two columns as 0 in the transformed matrix).