Q 4 ans is a^2+b^2+c^2d+^2How??? Here the term i is creating prob

Because this is a question of determinant..After cross multiplying and putting a negative sign as per the rule of solving a determinant you`ll get,[a^2-(i^2*b^2)] - [-c^2-(i^2*b^2)] ,,,,to which you`ll on solving get,. a^2+b^2+c^2+d^2..As i^2 == -1 i.e (minus1)