Вычислить sina, cos2a, если cosa = 5/13

и 0

Cosα=5/13 0<α<π/2 - 1-ая четверть

sinα=√ (1-cos²α) = √ (1 - (5/13) ²) = √ (1 - (25/169)) = √ (144/169) = 12/13

cos2α=cos²α - sin²α = (5/13) ² - (12/13) ² = (25/169) - (144/169) = - 119/169