Droped to 1 star based on no update/bug fixes This app needs an update. Lack of trig functions hinders its usefulness. Also the factoring is realy odd in some cases. I got this to check my answers in calculus with working derivatives and its help with some but due to reasons stated above this app fell short. Oh yeah and I dont think it has square root key either would be nice. So if I had to do it all again I would wait for the update.