UPDATED VERSION WITH BORDERS DRAWN BETWEEN RECTANGLES AND DETAILED EXPLANATIONS! The above is an extensive exploration of rectangular approximations to ares under a parabola utilizing the outstanding online graphing calculator, Desmos. CLICK on it to activate. In addition to a detailed overview and suggestions for the instructor, I've included a fleshed-out step-by-step activity for students which reflects my usual balance among the visual, symbolic, verbal and numerical- the Rule of Four... Please comment or use the new Contact Form in the sidebar to let me know if it's working properly and if you find it helpful. Your feedback is crucial to me. Use new contact form at top of right sidebar to contact me directly! If interested in purchasing my NEW 2012 Math Challenge Problem/Quiz book, click on BUY NOW at top of right sidebar. 175 problems divided into 35 quizzes with answers at back and DETAILED SOLUTIONS/STRATEGIES for the 1st 8 quizzes. Suitable for SAT I, Math I/II Subject Tests, Common Core Assessments, Math Contest practice and Daily/Weekly Problems of the Day. Includes multiple choice, case I/II/III type and constructed response items. Price is $9.95. Secured pdf will be emailed when purchase is verified.