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Consider a matrix  
The matrix A satisfies the equation 6A-1 = A2 + cA + dI, where c and d are scalars and I is the identity matrix. Then (c + d) is equal to
  • a)
    5
  • b)
    17
  • c)
    -6
  • d)
    11
Correct answer is option 'A'. Can you explain this answer?
Verified Answer
Consider a matrixThe matrix A satisfies the equation 6A-1= A2+ cA + dI...
Concept:
for the given square matrix, the characteristic equation will be
|B - AI| = 0
B = Given matrix
I = Unit matrix
A = Characteristic roots
Calculation:
|B - AI| = 0
Take the determinant of matrix, then 
(1 - A) [(4 - A) (1 - A) + 2] = 0
(1 - A) [4 - 4A - A + A2 + 2] = 0
(1 - A) [4 - 5A + A2 + 2] = 0
(1 - A) [A2 - 5A + 6] = 0
A2 - 5A + 6 - A3 + 5A2 - 6A = 0
-A3 + 6A2 - 11A + 6 = 0
A3 - 6A2 + 11A = 6
A2 - 6A + 11 = 6A-1       ........(1)
Given 6A-1 = A2 + cA + dI     .........(2)
Compare 1 and 2
c = -6, d = +11
c + d = +5
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Most Upvoted Answer
Consider a matrixThe matrix A satisfies the equation 6A-1= A2+ cA + dI...
Concept:
for the given square matrix, the characteristic equation will be
|B - AI| = 0
B = Given matrix
I = Unit matrix
A = Characteristic roots
Calculation:
|B - AI| = 0
Take the determinant of matrix, then 
(1 - A) [(4 - A) (1 - A) + 2] = 0
(1 - A) [4 - 4A - A + A2 + 2] = 0
(1 - A) [4 - 5A + A2 + 2] = 0
(1 - A) [A2 - 5A + 6] = 0
A2 - 5A + 6 - A3 + 5A2 - 6A = 0
-A3 + 6A2 - 11A + 6 = 0
A3 - 6A2 + 11A = 6
A2 - 6A + 11 = 6A-1       ........(1)
Given 6A-1 = A2 + cA + dI     .........(2)
Compare 1 and 2
c = -6, d = +11
c + d = +5
Free Test
Community Answer
Consider a matrixThe matrix A satisfies the equation 6A-1= A2+ cA + dI...
Concept:
for the given square matrix, the characteristic equation will be
|B - AI| = 0
B = Given matrix
I = Unit matrix
A = Characteristic roots
Calculation:
|B - AI| = 0
Take the determinant of matrix, then 
(1 - A) [(4 - A) (1 - A) + 2] = 0
(1 - A) [4 - 4A - A + A2 + 2] = 0
(1 - A) [4 - 5A + A2 + 2] = 0
(1 - A) [A2 - 5A + 6] = 0
A2 - 5A + 6 - A3 + 5A2 - 6A = 0
-A3 + 6A2 - 11A + 6 = 0
A3 - 6A2 + 11A = 6
A2 - 6A + 11 = 6A-1       ........(1)
Given 6A-1 = A2 + cA + dI     .........(2)
Compare 1 and 2
c = -6, d = +11
c + d = +5
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Consider a matrixThe matrix A satisfies the equation 6A-1= A2+ cA + dI, where cand dare scalars and Iis the identity matrix. Then (c+ d) is equal toa)5b)17c)-6d)11Correct answer is option 'A'. Can you explain this answer?
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