alleryTrace of matrix is sum of diagonal entries. For 2×2 [[a,b],[c,d]]:
Adet = ad - bc
Ba + b + c + d
Ca + d (= sum of eigenvalues)
Da × d
Answer & Solution
Correct answer: C. a + d (= sum of eigenvalues)
Trace = sum of diagonal = a + d.
Equals sum of eigenvalues.
**Cyclic invariance:** tr(AB) = tr(BA).
Trace is basis-independent.
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