Q43 / 124 · NTA Abhyas (JEE Main) 2020 · Mathematics · Determinants

Let A=a030b5-130c, where a,b,c are positive integers. If trA=7, then the greatest value of A is (where trA denotes the trace of matrix A i.e. the sum of principal diagonal elements of matrix A)

  • A
    6
  • B
    12
  • Correct answer
    C
    15
  • D
    10

Solution

trA=a+b+c=7
Ordered triplets of a,b,c are 1,1,5,1,2,4,1,3,3,2,1,4,2,2,3,2,3,2,2,4,1,3,1,3,3,2,2,3,3,1,4,1,2,4,2,1,5,1,1
A=a030b5-130c=abc+3b3=abc+b
A is greatest for 2,3,2 and equal to 15

Hence, the correct answer is option: 'C'.

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