NETMaths
Part BCSIR NET December 2023indefinite-implies-isotropic

Indefinite implies isotropic

Let (−, −) be a symmetric bilinear form on such that there exist nonzero with (v, v) > 0 > (w, w) and (v, w) = 0. Let A be the 2×2 real symmetric matrix representing this form in the standard basis. Which one of the following statements is true?

  1. A..
  2. B.rank A = 1.
  3. C.rank A = 0.
  4. D.There exists such that (u, u) = 0.

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The trap it tests

Converse assumed

The theorem runs one way. You used it in the other.

Drill statements like this

Related counterexample: Every real symmetric matrix is positive definite if det > 0

More on this topic

From Inner Product Spaces and FormsQuadratic forms, positive definiteness, Sylvester's law

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