After teaching at colleges in US as professor for 13 years and in New York public high school as a math teacher for 2 years, I retired from CUNY in 2009 and started to work as a Math and physics tutor, having improved many high school students' grades (in algebra,geometry, trigonometry, calculus and physics) and boosted their test scores in NY Regents, SAT Math, AP Calculus and AP Physics. When I tutor my students, I must first make sure they understand the concepts and be familiar with al...