Cos a = -0.8 найти tg2a

tg2a = (2*tg a)/(1 - tg²a);1 + tg²a = 1/cos²a;tg²a = (1/cos²a) - 1;При cos a = -0,8;tg²a = (1/(-0,8)²) - 1 = (1/0,64) - 1 = 0,5625;tg a = √tg²a = √0,5625 = 0,75;tg2a = 2*0,75/(1 - 0,5625) = 1,5/0,4375 = 15/10 : 4375/10000 = 15 * 1000/ 4375 = 15000/4375 = 24/7 = 3 3/7