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