Typing a sum into Google (or into your address bar) has always been a quick way to perform a calculation. That still works, but Google now displays a full-screen calculator for further mathematical fun when you do that kind of search.
As Google Operating System points out, for basic calculations actually typing your query will be quicker. However, if you want the more advanced trigonometry options, having an on-screen calculator could be useful. Note also that you need to select a function before you enter a number: to find the cosine of 90 degrees, you click cosine and then click on 90. (Also worth noting: the default option is radians, not degrees.)
New Interface for Google Calculator [Google Operating System]