JEE Main 2020
Matrices & Determinants
Matrices and Determinants
Easy
Question
The number of elements in the set \left\{ {A = \left( {\matrix{ a & b \cr 0 & d \cr } } \right):a,b,d \in \{ - 1,0,1\} \,and\,{{(I - A)}^3} = I - {A^3}} \right\}, where I is 2 2 identity matrix, is :
Answer: 3
Solution
This problem tests your understanding of matrix algebra, specifically the binomial expansion for matrices and the properties of idempotent matrices. We are given a condition involving a matrix and need to find the number of such matrices whose elements are restricted to .
1. Key Concept: Binomial Expansion for Matrices
For any two matrices and that commute (i.e., ), the binomial expansion formula holds: In our case, we have . Since the identity matrix commutes with any