This app was mentioned in 3 comments, with an average of 1.33 upvotes
Free Graphing Calculator 2 for Android (maybe there's an ios version, not sure). In addition to being a really nice scientific calculator, it also has a simplified math cheat sheet textbook built in so say you're trying to calculate an angle, rather than trying to remember trig class, just look in the trig section of the book. It's great for people like me who suck at math but need to use it almost constantly and often need to do really complex stuff or need to do the same things over and over.
Pretty sure this is the one I used https://play.google.com/store/apps/details?id=com.jockusch.freegraphingcalculator Not perfect but after you figure it out it's fine for at least calculus BC like I said
https://play.google.com/store/apps/details?id=com.jockusch.freegraphingcalculator&hl=en
It has graphing and so much more. Flip through the pictures!