a) (tg a - ctg a)^2 = 16 = (tg a)^2 + 2*tg a * ctg a + (ctg a)^2 = [ tg a * ctg a = 1] =
= (tg a)^2 + (ctg a)^2 +2 = 16
(tg a)^2 + (ctg a)^2 = 14
a) (tg a - ctg a)^2 = 16 = (tg a)^2 + 2*tg a * ctg a + (ctg a)^2 = [ tg a * ctg a = 1] =
= (tg a)^2 + (ctg a)^2 +2 = 16
(tg a)^2 + (ctg a)^2 = 14