id recommend using a cg50 personally. its quite expensive, but its saved me a million times. it draws polar graphs, integrates graphs, finds area of a region between equations, good for plotting polar graphs too,
and most importantly it can handle complex numbers more than the fx991-ex, it can do polar form, and exponenitals where i is on the power. extremely helpful in chapter 1 of core pure 2, the fx991-ex cant do that.