The projection of $\begin{pmatrix} -8 \\ b \end{pmatrix}$ onto $\begin{pmatrix} 2 \\ 1 \end{pmatrix}$ is
\[-\frac{13}{5} \begin{pmatrix} 2 \\ 1 \end{pmatrix}.\]Find $b.$
Question:
The projection of $\begin{pmatrix} -8 \\ b \end{pmatrix}$ onto $\begin{pmatrix} 2 \\ 1 \end{pmatrix}$ is
\[-\frac{13}{5} \begin{pmatrix} 2 \\ 1 \end{pmatrix}.\]Find $b.$
Answer:
Let's think step by step.

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3
The projection of $\begin{pmatrix} -8 \\ b \end{pmatrix}$ onto $\begin{pmatrix} 2 \\ 1 \end{pmatrix}$ is
\[-\frac{13}{5} \begin{pmatrix} 2 \\ 1 \end{pmatrix}.\]Find $b.$
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