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Find the matrix X so that X[123456]=[-7-8-9246] - Mathematics

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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 = 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 - Exercise 3.5 [Page 101]

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NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 3 Matrices
Exercise 3.5 | Q 11 | Page 101

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