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Let A=[aij]3×3A = [a_{ij}]_{3 \times 3} be a matrix, defined by aij={2i+3j,i<j6,i=j3i−2j,i>ja_{ij} = \begin{cases} 2i+3j & , i < j \\6 &, i=j\\ 3i-2j & , i > j \end{cases}. The number of elements in A which are greater than 6, is

Solution

✅ Correct Option: 3

The matrix has 9 positions (3 rows × 3 columns). For each position (i,j)(i,j):

  • Diagonal elements (i=j)(i = j): aij=6a_{ij} = 6
  • Above diagonal (i<j)(i < j): aij=2i+3ja_{ij} = 2i + 3j
  • Below diagonal (i>j)(i > j): aij=3i−2ja_{ij} = 3i - 2j

For Row 1 (i=1)(i = 1):

a11a_{11}: i=ji = j, so a11=6a_{11} = 6

a12a_{12}: i<ji < j (1<2)(1 < 2), so a12=2(1)+3(2)=2+6=8a_{12} = 2(1) + 3(2) = 2 + 6 = 8

a13a_{13}: i<ji < j (1<3)(1 < 3), so a13=2(1)+3(3)=2+9=11a_{13} = 2(1) + 3(3) = 2 + 9 = 11


For Row 2 (i=2)(i = 2):

a21a_{21}: i>ji > j (2>1)(2 > 1), so a21=3(2)−2(1)=6−2=4a_{21} = 3(2) - 2(1) = 6 - 2 = 4

a22a_{22}: i=ji = j, so a22=6a_{22} = 6

a23a_{23}: i<ji < j (2<3)(2 < 3), so a23=2(2)+3(3)=4+9=13a_{23} = 2(2) + 3(3) = 4 + 9 = 13


For Row 3 (i=3)(i = 3):

a31a_{31}: i>ji > j (3>1)(3 > 1), so a31=3(3)−2(1)=9−2=7a_{31} = 3(3) - 2(1) = 9 - 2 = 7

a32a_{32}: i>ji > j (3>2)(3 > 2), so a32=3(3)−2(2)=9−4=5a_{32} = 3(3) - 2(2) = 9 - 4 = 5

a33a_{33}: i=ji = j, so a33=6a_{33} = 6


The complete matrix is:

A=[68114613756]A = \begin{bmatrix} 6 & 8 & 11 \\ 4 & 6 & 13 \\ 7 & 5 & 6 \end{bmatrix}


Elements greater than 6:

a12=8a_{12} = 8 ✓

a13=11a_{13} = 11 ✓

a23=13a_{23} = 13 ✓

a31=7a_{31} = 7 ✓

The number of elements greater than 6 is 44.

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