Answer
As $v\rightarrow c^-, m\rightarrow \infty$
Work Step by Step
As $v\rightarrow c^-,$
$m\rightarrow \frac{m_0}{\sqrt{1-\frac{(c^-)^2}{c^2}}}=\frac{m_0}{\sqrt{1-\frac{(c^2)^-}{c^2}}}=\frac{m_0}{\sqrt{1-1^-}}=\frac{m_0}{0^+}=\infty$
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