JEE Main20207 Jan 2020Morning ShiftMathematicsMatricesActual
Let α be a root of the equation x 2 + x + 1 = 0 and the matrix A = 1 3 1 1 1 1 α α 2 1 α 2 α 4 , then the matrix A 31 is equal to
Options
- AA 3
- BI 3
- CA 2
- DA
Correct answer
A. A 3
Step-by-step solution
Here, α = ω , ω 2 where ω is complex cube root of unity. A 2 = 1 3 1 1 1 1 ω ω 2 1 ω 2 ω 1 1 1 1 ω ω 2 1 ω 2 ω = 1 0 0 0 0 1 0 1 0 ⇒ A 4 = 1 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 1 0 = 1 0 0 0 1 0 0 0 1 ⇒ A 31 = A 28 × A 3 = I × A 3 = A 3