Mathematics. According to the Institute of random estimates of TB, this is considered the matter of the toughest for 9 out of 10 students. If you have not changed much since the last calculus class I had, I imagine that it continues still very complicated today. Today Google launched a novelty that can help students who are experiencing a slight martyrdom in trying to understand it.
From today who place a well formatted equation in search of Google will see the results page is also a graph representing this equation. And you can use all sorts of functions, constants and mathematical operators from leveraging the sine, cosine, logarithms, pi and who knows what else. Just do not make putting a polynomial equation or crazy symbols that Google can not interpret. And of course, all must be entered in English. See this example and that other here for more details.
Remember, the Wolfram | Alpha, semantic search tool launched in 2009, already had this functionality since it debuted on the web and it can be much more complex to solve polynomial equations as well. So in a way Google is just balancing your side with something that has been done in search engines. But for students who need to understand math more easily remains one hand on the wheel.