JEE Main2013MathematicsMatricesActual
If P = 1 α 3 1 3 3 2 4 4 is the adjoint of a 3 × 3 matrix A and A = 4 , then α is equal to
Options
- A5
- B0
- C4
- D11
Correct answer
D. 11
Step-by-step solution
Given P = a d j A ⇒ P = a d j A = A 2 ∵     a d j A = A n - 1   where   n = 3 Now, P = 1 α 3 1 3 3 2 4 4 = 1 × 12 − 12 − α × 4 − 6 + 3 × 4 − 6 = 2 α - 6 ⇒ 2 α - 6 = 1 6 ⇒ α   =   11