# How to Factorise a Number (Or Check that is Prime) using a CASIO fx-83GT PLUS calculator

On the CASIO fx-83gt PLUS factorising is done like this:

• Entering the number,
• press equals,
• SHIFT and ., ,,, (this has “FACT” written above it in yellow).
• The Prime Factor Form is displayed as the answer.
• If the number is Prime, then the number itself is displayed.

This is a natural way to introduce what indices mean, because the CASIO gives the answers in index form eg 34 rather than 3x3x3x3

# Recommended Calculator CASIO fx-83GTX classwiz

I have a huge weakness for calculators, so if I see a new one that looks interesting, I usually buy it and see if it could replace my current favourite as my “Top Calculator”.

Since the launch of the CASIO fx-83GT range, the calculator market has been, for GCSE at least, a bit of a one-horse race. Several strong features are common across the whole market, they all basically do the job. What sets the 83GT apart is some unique features:

• The ability to factorise whole numbers (The FACT function). This is not only useful, but fun. What can be a dry subject to teach, suddenly becomes an area for experiemntation and competition, which happen to be my two favourite ways to spend time when I’m teaching Maths. The answers are expressed in Index Form so the pupil is taken straight to the gold standard of factorising numbers. So, I use it to teach index notation too. Factorising is crucial for a number of Mathematical areas, so it’s really nice that CASIO think it’s worthwhile to devote a function to it.
• Recurring decimals – well hidden above the “x squared” key, (it looks like a box with a dot on top), this function enables the pupil to type in recurring decimals. Answers can also be converted from recurring decimal, to fraction, to rounded decimal. Again, this encourages experimentation.

It will probably set you back about £12 depending on where you get it. There is a downloadable emulator on the casio website which is free for 90 days.

Update – Jan 2021 – The FX 83-GTX is even better than the FX 83-GT+ so I have switched over.

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