Consider the following matrix: A = [[2, 3],[x, y]] If the eigenvalues of A are 4 and 8, then: A. x = 4, y = 10 B. x = 5, y = 8 C. x = -3, y = 9 D. x = -4, y = 10
GATE 2010 · Engineering Mathematics · Eigen Value · easy
Answer: D. x = -4, y = 10
- Apply trace condition: y = 12 - 2 = 10.
- Apply determinant condition: 2*10 - 3*x = 32 => 20 - 3x = 32 => -3x = 12 => x = -4.
- Verify and state answer: Check: A = [[2,3],[-4,10]]. Trace = 12 = 4+8. Det = 20-(-12) = 20+12 = 32 = 4*8. Correct.