Don't use this function on the fx-991EX 

Yes the sequence needs to be 7/2 = Ans² SHIFT = to get the correct approximation, but as you suggest Scott, most people are just going to automatically go straight to press = as they are so used to it. The SD is then of course the function to use. I agree, it is probably best avoided as most are in the habit of pressing = and then pressing SD to get a decimal approximation.

The shift ≈ reruns the calculation just as = would. It's exactly what I would expect. I don't see the slightest problem here.

This is not a design error, it is just getting misused. If you calculate it once using the normal equal button, it will give you Ans^2=49/4, where Ans=7/2, but if you press the approximation button after pressing the normal equals, the ans variable changes to Ans=49/4, it is like having pressed the normal equals button twice . So, if you had pressed the approximation button from the start, the answer would've been what you would expect. The key is doing what it is supposed to do. The key's difference from the equals button is just that, in advance, it is telling the calculator that the answer should be in decimal, or approximated. Hope this was helpful!

The issue here is with the ANS variable, not the approx. equals (≈) - if you press the normal equals (=) then the answer will be the same, it recalculates for ANS. So if you want to have the approximate, you should press approx. equals (≈) right away, instead of the normal equals (=).

All calculators I've used do the same. Except Some calculators make it explicit which expression you are evaluating. TI Nspire, for example, always shows each evaluation in a new line, and instead of displaying Ans, it substitutes it with the actual value from the above evaluation.

The manual isn't especially explicit about this feature either (p.10): "While MathI/MathO or MathI/DecimalO is selected for Input/Output on setup menu, each press of [SD] will toggle the currently displayed calculation result between its fraction form and decimal form, its √ form and decimal form, or its π form and decimal form." Further down: "To obtain a decimal value calculation result while MathI/MathO or LineI/LineO is selected, press shift + [=] (≈) instead of [=] after inputting a calculation."

That's just because of how the equal key and and works, if you did 7 ÷ 2 and then ans squared and did shift equal you would get the right answer.

That is not a bug. You should use the approximate instead of =, not in addition to it. If you have the value on display then you should use S-D. However, if you want decimals it is best to set the output mode.

This could also be avoided if you sed the aproximation button insted of the = button dont kniw its name in english You did this ans^2=49/4 the hit the aproximation key and considering how thus calculator takes it the whole input you did would be this ans^2=49/4 Now ans equals to (49/4) and then this operation ans^2≈ and you got 150 something you basically asked the calculator to calculato 49/4 to the power of 2 and asked it to give you an anwer from that It should work if you did this instead Ans^2≈12.25 or around that

Hi sir, I have a question. What's the difference between the - negative sign and the (-) negative sign?

1) thanks 2) well, if there are 2 keys, there must be a difference between the two 3) Casio is used to put a lot of similar key that really baffle anyone who is not super inside not only math itself, but also how IA solve math problems... and it s not very useful for a student or someone that "uses" math but does not go to sleep thinking at 6th dimension graphs.

Thank you

Make video in comparison of 991 ex vs 991es plus.

Is 991ex a programmable calculator?

Clean it! - Look at the state of that Solar cell..