If you are able, please purchase a handheld, one-line, scientific calculator like the TI-30Xa which costs about $9 at Walmart.
Otherwise, you can use an online calculator such as those linked below.
Most online calculators and calculator apps are TWO-line calculators. So make sure that you are using a ONE-line calculator because the calculator you will be given to use on the Geometry EOC is a TI-30Xa which is a ONE-line calculator and is more difficult to use.