Let $A = [a_{ij}]_{3×3}$ be a matrix, defined by $a_{ij}=\left\{\begin{matrix}2i+3j,&i<j\\6,&i=j\\3i-2j,&i>j\end{matrix}\right.$. The number of elements in A which are greater than 6, is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 4
Matrix is defined as:
$a_{ij}=\begin{cases} 2i+3j , & ij \end{cases}$
For $3\times 3$ matrix:
$A=\begin{bmatrix} a_{11} & a_{12} & a_{13} \\ a_{21} & a_{22} & a_{23} \\ a_{31} & a_{32} & a_{33} \end{bmatrix}$
Now, compute each element:
$a_{11}=6$
$a_{12}=2(1)+3(2)=2+6=8$
$a_{13}=2(1)+3(3)=2+9=11$
$a_{21}=3(2)-2(1)=6-2=4$
$a_{22}=6$
$a_{23}=2(2)+3(3)=4+9=13$
$a_{31}=3(3)-2(1)=9-2=7$
$a_{32}=3(3)-2(2)=9-4=5$
$a_{33}=6$
So,
$A=\begin{bmatrix} 6 & 8 & 11 \\ 4 & 6 & 13 \\ 7 & 5 & 6 \end{bmatrix}$
Elements greater than 6 are: $8, 11, 13, 7$
Number of such elements = $4$