This is going to sound really geeky but, if you own an fx-82es, fx-83es or fx-85es, you can upgrade it to a fx911es, which is soo much better. It allows you to integrate/differentiate/solve quadratic equation etc.
1. Check what version you have - on the back, just above the made in China sign, there is a letter in a circle: if it’s a B, unlucky because you can’t do the mod, however if it’s an A you can.
2. Open up your calculator - on the back there are six screws, using a Phillips screw driver, remove these and then lift off the back, revealing the circuit board.
3. Find the P4 jumper - on the circuit board there are six screws, between the middle two is a little white P4, to the right of this is a small split silver circle. Take your graphite pencil and colour this, making sure the whole thing is covered.
4. Put it back together-now put the back, back on and screw the screws into the holes.
This procedure basically makes the calculator confuse itself about which model it is; models only differ at the jumps. Casio did this to make the calculator suitable for all exams, as in China, you can't use an fx-991es in an exam.