TR3.5

Exr0n

Exr0n 2021-09-27 Mon 12:00

1 #exercise 2.A.17

  • All polynomials have \((x+2)\) as a factor, and therefore can be written in the form \((x+2)f_j(x)\) where \(f_j(x)\) has degree at most \(m-1\).
  • Because the \(z^0, z^1, ..., z^{m-1}\) is a spanning list of \(P_m-1(F)\), the spanning list of \(P_{m-1}(F)\) is of length \(m\).
  • The original list had \(m+1\) elements, so by Axler 2.23 the list cannot be linearly independent.
  • We can therefore find a non-trivial combination that equals zero, and can thus find a non-trivial combination of the original list by multiplying each vector by \((x-2)\).

2 Elementary Matrices

#incomplete

2.1 Things you can do

  • Multiply a row by a nonzero scalar
  • Add two rows
  • Switch the ordering of the rows

The matrices that correspond to these operations are what we call #definition elementary matrices.

This includes the identity matrix (multiply by the scalar 1).