1. The problem statement, all variables and given/known data 2. Relevant equations Reduce the matrix to reduced matrix by removing 1 row completely Number of trees = determinant of [ Ar times ArT ] 3. The attempt at a solution I removed 4th row to get Ar(reduced matrix) Then I did Ar times Ar (transpose) And found it's determinant but I got different answer depending on which row I remove. Do I randomly remove any row? Sorry for posting too many homework questions. I have an exam coming up in Feb.