def triangle_by_angles(a, b, c):
    if a <= 0 or b <= 0 or c <= 0:
        return "Ошибка: стороны должны быть положительными"
    if a + b <= c or a + c <= b or b + c <= a:
        return "Ошибка: такого треугольника не существует"
 
    sides = sorted([a, b, c])
    a2 = sides[0]**2
    b2 = sides[1]**2
    c2 = sides[2]**2
 
    if a2 + b2 == c2:
        return "Прямоугольный"
    elif a2 + b2 > c2:
        return "Остроугольный"
    else:
        return "Тупоугольный"
 
# Примеры
print(triangle_by_angles(3, 4, 5))   # Прямоугольный
print(triangle_by_angles(5, 5, 5))   # Остроугольный
print(triangle_by_angles(3, 4, 6))   # Тупоугольный

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