JEE Main · 2019 · 12 Apr 2019 · Shift 1 · Matrices

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If is the inverse of a matrix , then the sum of all values of for which , is :
  1. (A)0
  2. (B)-1
  3. (C)1✓ Correct
  4. (D)2

Answer: (C)

Solution

Since , we have , so . Expanding along its first row, . The condition means , hence , so , i.e. or . By Vieta's formulas the two values of add up to .

JEE Main · 2019 · 12 Apr 2019 · Shift 1 · Single correct option

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