side view of math formulas and calculation written over chalboard. selective focus.

background, number, high, sign, board, pattern, medicine, formula, symbol, backdrop, concept, school, complex, exam, education, studying, science, learn, problem, solution, geometry, study, college, University, lesson, knowledge, write, physics, theory, teach, mathematics, slate, teacher, class, blackboard, mathematical, algebra, scribble, proof, plus, minus, classroom, calculate, chalk, students, lecture, calculus, math, chalkboard, trigonometry,