JEE Main 2019 Mathematics question
If is the inverse of a 3 × 3 matrix A, then the sum of all values of α for which det(A) + 1 = 0, is:
Answer: (D)
Solution
det B = 2α − 2α − 25 = −1 ⇒ α − α − 12 = 0; sum of roots 1. (The first row is cut in the source; the official matrix is used.)