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Find the matrix X so that X[(1, 2, 3),(4, 5, 6)]= [(–7, –8, –9),(2, 4, 6)]

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Question

Find the matrix X so that X`[(1, 2, 3),(4, 5, 6)]= [(-7, -8, -9),(2, 4, 6)]`

Sum
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Solution

X = `[(a, b),(c, d)]`

X`[(1, 2, 3),(4, 5, 6)] = [(a, b),(c, d)][(1, 2, 3),(4, 5, 6)]`

= `[(a + 4b, 2a + 5b, 3a + 6b),(c + 4d, 2c + 5d, 3c + 6d)]`

= `[(-7, -8, -9),(2, 4, 6)]`   ...(Given)

Keeping corresponding elements same,

  a + 4b = –7   ...(1)
2a + 5b = –8   ...(2)
 –     –      +   
3a + 6b = –9   ...(3)

Multiplying equation (1) by 2 and subtracting it from equation (2),

2a + 8b = –14
2a + 5b = –8
–       –      + 
        3b = –6
          b = –2

Putting the value of b in equation (3),

3a + 6 × (–2) = –9

3a – 12 = –9

3a = 12 – 9

3a = 3

a = 1

Keeping the corresponding elements of the second row same,

c + 4d = 2   ...(4)
2c + 5d = 4    ...(5)
3c + 6d = 6   ...(6)

On multiplying equation (4) by 2 and subtracting it from equation (5), we get

2c + 8d = 4
2c + 5d = 4
 –     –      +
        3d = 0
          d = 0

Putting the value of d in equation (6),

3c = 6

c = 2

Hence, X = `[(1, -2), (2, 0)]`.

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Chapter 3: Matrices - Miscellaneous Exercise on Chapter 3 [Page 73]

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NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 3 Matrices
Miscellaneous Exercise on Chapter 3 | Q 8. | Page 73

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