diff --git a/src/lib.rs b/src/lib.rs
index ec2bc62..9896c49 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -184,9 +184,8 @@ impl Matrix {
             return Err(MatrixError::InvalidDataSize);
         }
 
-        for i in 0..self.columns {
-            self.data.insert((i * self.columns) + i, data[i]);
-        }
+        let pos = index * self.columns;
+        self.data.splice(pos..pos, data);
 
         self.rows += 1;
 
@@ -202,7 +201,7 @@ impl Matrix {
             return Err(MatrixError::IndexOutOfRange);
         }
 
-        if end.0 >= self.rows || end.1 >= self.columns {
+        if end.0 > self.rows || end.1 > self.columns {
             return Err(MatrixError::IndexOutOfRange);
         }
 
@@ -219,8 +218,8 @@ impl Matrix {
         }
 
         let new_matrix = Matrix {
-            rows: (end.0 + 1) - start.0,
-            columns: (end.1 + 1) - start.1,
+            rows: end.0 - start.0,
+            columns: end.1 - start.1,
             data: new_data,
         };
 
@@ -1870,4 +1869,263 @@ mod tests {
             vec![Fraction::from(1), Fraction::from(9), Fraction::from(2),]
         );
     }
+
+    #[test]
+    fn test_insert_row_basic_middle() {
+        let mut m = Matrix {
+            rows: 2,
+            columns: 2,
+            data: vec![
+                Fraction::from(1),
+                Fraction::from(2),
+                Fraction::from(3),
+                Fraction::from(4),
+            ],
+        };
+
+        let new_row = vec![Fraction::from(9), Fraction::from(9)];
+
+        m.insert_rows(1, new_row.clone()).unwrap();
+
+        assert_eq!(m.rows, 3);
+
+        assert_eq!(m.get_row(1).unwrap().cloned().collect::<Vec<_>>(), new_row);
+    }
+
+    #[test]
+    fn test_insert_row_at_start() {
+        let mut m = Matrix::new(2, 2, Fraction::from(1)).unwrap();
+
+        let new_row = vec![Fraction::from(5), Fraction::from(6)];
+
+        m.insert_rows(0, new_row.clone()).unwrap();
+
+        assert_eq!(m.get_row(0).unwrap().cloned().collect::<Vec<_>>(), new_row);
+    }
+
+    #[test]
+    fn test_insert_row_invalid_index() {
+        let mut m = Matrix::new(2, 2, Fraction::from(0)).unwrap();
+
+        let data = vec![Fraction::from(1), Fraction::from(2)];
+
+        let result = m.insert_rows(2, data);
+
+        assert!(matches!(result, Err(MatrixError::RowOutOfRange)));
+    }
+
+    #[test]
+    fn test_insert_row_invalid_size() {
+        let mut m = Matrix::new(2, 3, Fraction::from(0)).unwrap();
+
+        let data = vec![Fraction::from(1), Fraction::from(2)];
+
+        let result = m.insert_rows(1, data);
+
+        assert!(matches!(result, Err(MatrixError::InvalidDataSize)));
+    }
+
+    #[test]
+    fn test_insert_row_preserves_other_rows() {
+        let mut m = Matrix {
+            rows: 2,
+            columns: 2,
+            data: vec![
+                Fraction::from(1),
+                Fraction::from(2),
+                Fraction::from(3),
+                Fraction::from(4),
+            ],
+        };
+
+        let new_row = vec![Fraction::from(9), Fraction::from(9)];
+
+        m.insert_rows(1, new_row).unwrap();
+
+        assert_eq!(
+            m.get_row(0).unwrap().cloned().collect::<Vec<_>>(),
+            vec![Fraction::from(1), Fraction::from(2)]
+        );
+
+        assert_eq!(
+            m.get_row(2).unwrap().cloned().collect::<Vec<_>>(),
+            vec![Fraction::from(3), Fraction::from(4)]
+        );
+    }
+
+    #[test]
+    fn test_insert_row_multiple_times() {
+        let mut m = Matrix::new(2, 2, Fraction::from(0)).unwrap();
+
+        let r1 = vec![Fraction::from(1), Fraction::from(1)];
+        let r2 = vec![Fraction::from(2), Fraction::from(2)];
+
+        m.insert_rows(1, r1).unwrap();
+        m.insert_rows(2, r2.clone()).unwrap();
+
+        assert_eq!(m.get_row(2).unwrap().cloned().collect::<Vec<_>>(), r2);
+    }
+
+    #[test]
+    fn test_insert_row_consistency_with_get() {
+        let mut m = Matrix::new(2, 3, Fraction::from(0)).unwrap();
+
+        let new_row = vec![Fraction::from(10), Fraction::from(20), Fraction::from(30)];
+
+        m.insert_rows(1, new_row.clone()).unwrap();
+
+        for (i, val) in new_row.iter().enumerate() {
+            assert_eq!(*m.get(1, i).unwrap(), *val);
+        }
+    }
+
+    #[test]
+    fn test_insert_row_single_column() {
+        let mut m = Matrix {
+            rows: 2,
+            columns: 1,
+            data: vec![Fraction::from(1), Fraction::from(2)],
+        };
+
+        let new_row = vec![Fraction::from(9)];
+
+        m.insert_rows(1, new_row).unwrap();
+
+        assert_eq!(
+            m.data,
+            vec![Fraction::from(1), Fraction::from(9), Fraction::from(2),]
+        );
+    }
+
+    #[test]
+    fn test_sub_matrix_basic() {
+        let m = Matrix {
+            rows: 3,
+            columns: 3,
+            data: vec![
+                Fraction::from(1),
+                Fraction::from(2),
+                Fraction::from(3),
+                Fraction::from(4),
+                Fraction::from(5),
+                Fraction::from(6),
+                Fraction::from(7),
+                Fraction::from(8),
+                Fraction::from(9),
+            ],
+        };
+
+        let sub = m.sub_matrix((0, 0), (2, 2)).unwrap();
+
+        // Esperado (end exclusivo):
+        assert_eq!(sub.rows, 2);
+        assert_eq!(sub.columns, 2);
+
+        assert_eq!(
+            sub.data,
+            vec![
+                Fraction::from(1),
+                Fraction::from(2),
+                Fraction::from(4),
+                Fraction::from(5),
+            ]
+        );
+    }
+
+    #[test]
+    fn test_sub_matrix_middle() {
+        let m = Matrix {
+            rows: 4,
+            columns: 4,
+            data: (1..=16).map(Fraction::from).collect(),
+        };
+
+        let sub = m.sub_matrix((1, 1), (3, 3)).unwrap();
+
+        assert_eq!(sub.rows, 2);
+        assert_eq!(sub.columns, 2);
+
+        assert_eq!(
+            sub.data,
+            vec![
+                Fraction::from(6),
+                Fraction::from(7),
+                Fraction::from(10),
+                Fraction::from(11),
+            ]
+        );
+    }
+
+    #[test]
+    fn test_sub_matrix_single_element() {
+        let m = Matrix::new(3, 3, Fraction::from(5)).unwrap();
+
+        let sub = m.sub_matrix((1, 1), (2, 2)).unwrap();
+
+        assert_eq!(sub.rows, 1);
+        assert_eq!(sub.columns, 1);
+        assert_eq!(sub.data, vec![Fraction::from(5)]);
+    }
+
+    #[test]
+    fn test_sub_matrix_invalid_start() {
+        let m = Matrix::new(2, 2, Fraction::from(0)).unwrap();
+
+        let result = m.sub_matrix((2, 0), (3, 1));
+
+        assert!(matches!(result, Err(MatrixError::IndexOutOfRange)));
+    }
+
+    #[test]
+    fn test_sub_matrix_invalid_end() {
+        let m = Matrix::new(2, 2, Fraction::from(0)).unwrap();
+
+        let result = m.sub_matrix((0, 0), (3, 3));
+
+        assert!(matches!(result, Err(MatrixError::IndexOutOfRange)));
+    }
+
+    #[test]
+    fn test_sub_matrix_invalid_range() {
+        let m = Matrix::new(3, 3, Fraction::from(0)).unwrap();
+
+        let result = m.sub_matrix((2, 2), (1, 1));
+
+        assert!(matches!(result, Err(MatrixError::IndexOutOfRange)));
+    }
+
+    #[test]
+    fn test_sub_matrix_full_copy() {
+        let m = Matrix {
+            rows: 2,
+            columns: 2,
+            data: vec![
+                Fraction::from(1),
+                Fraction::from(2),
+                Fraction::from(3),
+                Fraction::from(4),
+            ],
+        };
+
+        let sub = m.sub_matrix((0, 0), (2, 2)).unwrap();
+
+        assert_eq!(sub.data, m.data);
+    }
+
+    #[test]
+    fn test_sub_matrix_consistency_with_get() {
+        let m = Matrix {
+            rows: 3,
+            columns: 3,
+            data: (0..9).map(Fraction::from).collect(),
+        };
+
+        let sub = m.sub_matrix((0, 0), (3, 3)).unwrap();
+
+        for r in 0..sub.rows {
+            for c in 0..sub.columns {
+                assert_eq!(*sub.get(r, c).unwrap(), *m.get(r, c).unwrap());
+            }
+        }
+    }
 }