\[\mathbf{Найдем\ синус.}\]
\[1)\cos a = 1:\]
\[\sin^{2}a = 1 - \cos^{2}a = 0\]
\[\sin a = \pm \sqrt{0} = 0.\]
\[2)\cos a = 0:\]
\[\sin^{2}a = 1 - \cos^{2}a = 1\]
\[\sin a = \pm \sqrt{1} = \pm 1.\]
\[Найдем\ тангенс.\]
\[1)\ ctg\ a = 1:\]
\[tg\ a = \frac{1}{\text{ctg\ a}} = 1.\]
\[2)\ ctg\ a = - \frac{1}{3}:\]
\[tg\ a = \frac{1}{\text{ctg\ a}} = - 3.\]