Решение задания приложено
cos(A+B) = cosA•cosB-sinA•sinB
sin A = ✓1-(25/169) = ✓144/169 = 12/13
cos B = ✓1-(4/5)² = ✓1-(16/25) = ✓9/25 = -3/5
cos(A+B) = 5/13•(-3/5)+12/13•4/5 = -3/13+48/65 = 48-15/65 = 33/65
Решение задания приложено
cos(A+B) = cosA•cosB-sinA•sinB
sin A = ✓1-(25/169) = ✓144/169 = 12/13
cos B = ✓1-(4/5)² = ✓1-(16/25) = ✓9/25 = -3/5
cos(A+B) = 5/13•(-3/5)+12/13•4/5 = -3/13+48/65 = 48-15/65 = 33/65