The projection of $\begin{pmatrix} a \\ 7 \end{pmatrix}$ onto $\begin{pmatrix} -1 \\ 4 \end{pmatrix}$ is
\[\frac{26}{17} \begin{pmatrix} -1 \\ 4 \end{pmatrix}.\]Find $a.$
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The projection of $\begin{pmatrix} a \\ 7 \end{pmatrix}$ onto $\begin{pmatrix} -1 \\ 4 \end{pmatrix}$ is
\[\frac{26}{17} \begin{pmatrix} -1 \\ 4 \end{pmatrix}.\]Find $a.$
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
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user
2
The projection of $\begin{pmatrix} a \\ 7 \end{pmatrix}$ onto $\begin{pmatrix} -1 \\ 4 \end{pmatrix}$ is
\[\frac{26}{17} \begin{pmatrix} -1 \\ 4 \end{pmatrix}.\]Find $a.$
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