\input arrows.tex $$ \vcenter { \def \hfq {\hfil \ } \offinterlineskip \halign { % preamble &\hfq #\hfq \cr $t$& \vrule depth 5pt & $-\infty $&& $-7/3$&& $0$&& $1$&& $+\infty $& \cr \noalign{\hrule} $x' (t)$& \vrule height 10pt depth 3pt & & $-$& $\approx -9, 33$& $-$& $0$& $+$& $1$& $+$&& \cr \noalign{\hrule} \bbuucenter{$x (t)$}& \vrule& \bbuup{$+\infty $}& \bbup{\brightdownarrow} & \bup{$\approx 14, 9$}& \brightdownarrow & \down{$4\strut $}& \bbrightuparrow & \bbup{$6$}& \bbup {\bbrightuparrow }& \bbup {\bbup {$+\infty $}} \cr \noalign{\hrule} $y' (t)$& \vrule height 10pt depth 3pt & & $+$& $0$& $-$& $-7$& $-$& $0$& $+$&& \cr \noalign{\hrule} \bbuucenter{$y (t)$}& \vrule& \down {$-\infty $}& \brightuuparrow & \bbuup {$\approx 18, 52$}& \bbup {\brightdownarrow }& \bbup {$4$}& \brightdownarrow & \down{$0$}& \bbrightuuparrow & \bbuup{$+\infty $} \cr }} $$ \bye