Whilst helping my sis-in-law do some maths revision we were doing squares/cubes/roots, and I noticed her calculator seemed to be giving an incorrect answer.

For the calculation “-3 squared = ?”, it answered “-9”, for the calculation “-3 x -3 = ?” it also gave “-9”.

I know that’s incorrect but does anyone here with kids know if the calculator has some weird operating modes that may have done this?

It’s Casio FX83-ES, I gather it’s a fairly normal/popular scientific calculator now.
The negative symbol was added using the specific -Ve button!

Can you try using brackets to force it to give the correct answer?

For “-3 squared = ?”, I suspect it’s doing -(3^2) rather than (-3)^2

Well to be brutally honest the first question I’d ask is why both you and she are using a calculator for such a simple sum as it will get in the way of learning about power functions.

Have a look here for instructions as it is almost certainly user error.

http://www.york.ac.uk/media/studenthome/studying/examsandassessments/student/calculator/instructions.pdf

Oh and you are hitting the “=” button, not the ANS button?

You will need to use brackets. The calculator will do the indices before applying any functions due to BIDMAS and so without any brackets will calculate -(3^2).

Are you getting -2 by typing [-] and then [3], or by typing [3] and then the change symbol [+/-] ?

I’ve just had a play on my trusty Casio FX451, and I can’t find any combination of keypresses which give the answer you’re getting.

Belay that, I’ve just skimmed the instructions on the link provided above.

You can type the convenient keystroke [shift] [9] CLR [3] All [Menu] Yes to reinitialise the calculator. I’d do that, make sure it’s not in some sort of random wacky mode that’s expecting Reverse Polish Notation or something equally hoary.

gonefishin –
Well to be brutally honest the first question I’d ask is why both you and she are using a calculator for such a simple sum as it will get in the way of learning about power functions.

Ooh get you – thanks! Firstly, for a number of reasons she struggles with maths and praise to her for trying in adulthood to improve! Secondly my degree included further engineering mathematics so I can quite easily cope, cheers!

The example I gave was just an example, but i’ll try out the different options as suggested, it is bringing back memories of the opposing ways that sharp/casio calculators worked from yesteryear so will double-check – cheers all.

As others have said, there’s nothing wrong with your calculator. It’s calculating the powers and then multiplying by -1. Technically, of course, neither method is incorrect but by convention we implicitly add brackets around the (-3).

My calculator does the same thing.

The calculator parses the input “-3²” as “-1 x (3 x 3)”, ie “-1 x 9”.

The correct syntax is “(-3)²”, which is interpreted as “-3 * -3”, ie 9.

Would pressing [=] before pressing [x²] not achieve the same result and avoid having to cock about with parentheses?

Yep. The idea of the Casio is that you write the whole expression in first and then hit equals. It’s a brilliant system.

What exactly is further engineering mathematics?

Hmmm ok thanks – have to admit I didn’t think it would apply an order to such a simple operation.
She is familiar with BIDMAS principles so will just let her know to follow that as normal.

From memory, Eng. maths was just stuff that came in useful later for more detailed engineering work – thermo/aero-dynamics, etc. Laplace & Z-transforms, matrices, fourier series, linear optimisations, stats, etc…
And is then forgetten within a year of starting work as everything is done in software packages instead! But at least you know the principles. In theory…