Question

Найдите Sin A и Tg A, если Cos A = 2/7

Answer 1

cos A = 2/7           0 < A < π/2 (I четверть)
sin^2 A = 1 - cos^2 A = 1 - (2/7)^2 = 1 - 4/49 = 45/49 => cos √45/√49 = 3√5/7
tg A = sin A/cos A  = 3√5 · 2 / 7 · 7 = 6√5/49