Question

tg a * корень из (1-ctg^2a)

Answer 1

1+ctg^2 a =1/sin^2 a =>
-ctg^2 a =1-1/sin^2 a
tg a =sina / cos a =>
$sin a/cos a*sqrt{1-1+1/sin^2a} = sin a / cos a *1/sin a =1/cos a$