\(5x^2+21x+v\) \(=0\)
\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)
\(x = {-21 \pm \sqrt{21^2-20v} \over 10}\)
\( {-21 \pm \sqrt{21^2-20v} \over 10}= {-21 \pm \sqrt{301} \over 10}\)
\(\sqrt{21^2-20v}=\sqrt{301}\)
\(21^2-20v=301\)
\(301-21^2=-20v\)
\(v=\frac{-140}{-20}=7\)
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