Show that there do not exist scalars c1, c2, and c3 such that c1(1, 0, 1, 0) + c2(1, 0, -2, 1) + c3(2, 0, 1, 2) = (1, -2, 2, 3)

Respuesta :

Write the system in augmented-matrix form:

[tex]c_1(1,0,1,0)+c_2(1,0,-2,1)+c_3(2,0,1,2)=(1,-2,2,3)[/tex]

[tex]\iff\left[\begin{array}{ccc|c}1&1&2&1\\0&0&0&-2\\1&-2&1&2\\0&1&2&3\end{array}\right][/tex]

Row reduce this matrix:

  • Add -1(row 1) to row 3:

[tex]\left[\begin{array}{ccc|c}1&1&2&1\\0&0&0&-2\\0&-3&-1&1\\0&1&2&3\end{array}\right][/tex]

  • Add 3(row 4) to row 3:

[tex]\left[\begin{array}{ccc|c}1&1&2&1\\0&0&0&-2\\0&0&5&10\\0&1&2&3\end{array}\right][/tex]

  • Multiply row 3 by 1/5:

[tex]\left[\begin{array}{ccc|c}1&1&2&1\\0&0&0&-2\\0&0&1&2\\0&1&2&3\end{array}\right][/tex]

  • Add -2(row 3) to row 4:

[tex]\left[\begin{array}{ccc|c}1&1&2&1\\0&0&0&-2\\0&0&1&2\\0&1&0&-1\end{array}\right][/tex]

  • Add -2(row 3) and -1(row 4) to row 1:

[tex]\left[\begin{array}{ccc|c}1&0&0&-2\\0&0&0&-2\\0&0&1&2\\0&1&0&-1\end{array}\right][/tex]

This matrix tells us that [tex]c_1=-2[/tex], [tex]c_2=-1[/tex], and [tex]c_3=2[/tex], but clearly [tex]0c_1+0c_2+0c_3=0\neq-2[/tex], so there is no solution.

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