Which of the following are correct? (A) If A and B are symmetric matrices such that AB = BA, then AB is symmetric. Choose the correct answer from the options given below: |
(A) and (B) only (A), (B) and (C) only (A), (B), (C) and (D) (C) and (D) only |
(A) and (B) only |
The correct answer is Option (1) → (A) and (B) only $\text{(A) }A,B\ \text{symmetric and }AB=BA$ $(AB)^{T}=B^{T}A^{T}=BA=AB\ \Rightarrow\ AB\ \text{symmetric. True.}$ $\text{(B) }A,B\ \text{symmetric of same order}$ $(A+B)^{T}=A^{T}+B^{T}=A+B\ \Rightarrow\ \text{symmetric. True.}$ $\text{(C) }A,B\ \text{symmetric}$ $(AB-BA)^{T}=B^{T}A^{T}-A^{T}B^{T}=BA-AB=-(AB-BA)\ \Rightarrow\ \text{skew-symmetric, not symmetric. False.}$ $\text{(D) }A,B\ \text{symmetric}$ $(AB+BA)^{T}=B^{T}A^{T}+A^{T}B^{T}=BA+AB=AB+BA\ \Rightarrow\ \text{symmetric, not skew-symmetric. False.}$ |