Q28 / 124 · NTA Abhyas (JEE Main) 2020 · Mathematics · Determinants

Let a, b and c are the roots of the equation x3-7x2+9x-13=0 and A and B are two matrices given by A=abcbcacab and B=bc-a2ca-b2ab-c2ca-b2ab-c2bc-a2ab-c2bc-a2ca-b2, then the value of AB is equal to

  • A
    -154
  • Correct answer
    B
    -1543
  • C
    -22
  • D
    -223

Solution

a+b+c=7
ab+bc+ca=9
abc=13
B is the cofactor matrix of A⇒B=A2
⇒A⋅B=A3….i
A=abcbcacab=abc-a2-bb2-ac+cab-c2=3abc-a3-b3-c3
=-a+b+ca+b+c2-3ab+bc+ca
=-749-27
=-154
From i
BA=A3=-1543

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

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