AQA A-Level Further Maths C9-02 Factorisation of Determinants: Example 1

[meteoktem]

Thank you these types of examples were hard to find

[lefebvrejulien]

Thanks a lot sir ! Could we've done the subtraction of the third column by the second column at 3:44 ? Then we would have a upper triangular matrix and the determinant would have been the product of the terms of the diagonal ?