NTA Abhyas JEE Main2020MathematicsMatricesPractice
Let A and B are 3 × 3 matrices with real number entries, where A is symmetric, B is skew-symmetric and A + B A - B = A - B A + B . If A B T = - 1 k A B , then the sum of all possible integral value of k in 2 , 10 is equal to (where A T represent transpose of matrix A )
Options
- A20
- B24
- C28
- D45
Correct answer
B. 24
Step-by-step solution
A T = A , B T = - B A + B A - B = A - B A + B ⇒ A 2 - A B + B A - B 2 = A 2 + A B - B A - B 2 ⇒ A B = B A … … i Now, A B T = B T A T = - B A = - A B = - 1 k A B ⇒ k is an odd number ⇒ k = 3 , 5,7 , 9 Sum = 24