If you ask a group of teenagers what subject is the most difficult, odds are most will say math. Sure arithmetic and even algebra isn’t that bad. But once you cross the line into trigonometry and calculus, everything you thought you knew about math goes right out the window. Thankfully, we have the Internet and YouTube to help us with our school work. Casually Explained explains how to solve nearly any calculus problem in just 20 seconds with this one trick.