Ключевые слова: academic, blackboard, board, calculate, chalk, chalkboard, class, classroom, closeup, college, communication, complex, drawing, education, educator, elementary, equation, formula, green, hand, handwriting, help, information, knowledge, learn, learning, lecture, lesson, message, pointing, presentation, primary, professor, school, showing, sign, solution, student, study, studying, symbol, teach, teacher, teaching, theory, trigonometry, tutor, university, write, young,