а) cos a = - √(1 - 1/4) = - √3 / 2

tg a = sin a / cos a = - 1/2 * 2/√3 = - √3/3

ctg a = 1 / tg a = - 3/√3 = - √3

б)

sin a = - √( 1 - 1/9) = - √8/3

tg a = sin a / cos a = 1/2 * 3/√8 = 3/ 2√8 = 3/4√2 = 3√2/8

ctg a = 1/tga = 8 / 3√2 = 4√2/3

Использованы формулы:

sin²a + cos²a = 1

tg a = 1 / ctg a = sin a / cos a