Sin a,tg a,ctg a,если cos a=-0,8, П/2

Известен cos(a)
$sin^{2}(a)+cos^{2}(a) = 1 \\ sin(a) = \sqrt{1-cos^{2}(a)} \\ tg(a) = \frac{sin(a)}{cos(a)} \\ ctg(a) = \frac{1}{tg(a)}\\$
$cos(a) = -0.8 \\ sin(a) = \frac{+}{} 0.6\\ tg(a) = \frac{+}{} 0.75\\ ctg(a) = \frac{+}{} \frac{4}{3} \\$
$cos(a) = \frac{ \pi }{2} \\ sin(a) = \frac{+}{} \sqrt{1- \frac{\pi^{2}}{4} } \\ tg(a) = \frac{+}{} \frac{ \sqrt{1- \frac{\pi^{2}}{4} } }{\frac{\pi}{2}}\\ ctg(a) = \frac{+}{} \frac{ \frac{\pi}{2}}{ \sqrt{1- \frac{\pi^{2}}{4} }}\\$