Ключевые слова: adult, beard, blackboard, boys, brown hair, casual clothing, cheerful, child, classroom, concentration, confidence, copy space, education, formula, happiness, holding, indoors, intelligence, learning, lifestyles, looking, looking at camera, mathematical symbol, mathematics, men, occupation, one person, part of, portrait, real people, smiling, solution, standing, student, studying, success, teacher, teaching, teamwork, working, young adult,