Ctg1200,tg750,tg(-870),cos330,cos(-1230)

ctg1200 = сtg(360 * 3 + 120) = ctg120 = -1/sqrt3 = -sqrt3/3;tg750 = tg(360 * 2 + 30) = tg30 = 1/sqrt3 = sqrt3/3;tg(-870) = -tg870 = -tg(360 * 2 + 150) = -tg150 = -(-1/sqrt3) = 1/sqrt3 = sqrt3/3;cos330 = cos (360 - 30) = -cos30 = - sqrt3/2;cos(-1230) = cos1230 = cos(360 * 2 + 150) = cos150 = -sqrt3/2.