Why are Negative exponents creating syntax error where as positive exponents work fine.

The "syntax error" message that you are seeing on your Casio fx-991EX ClassWiz calculator is likely caused by the fact that the calculator does not support the use of decimal values in the exponent. The calculator can only accept integers (whole numbers) as exponents.
To work around this issue, you can try rounding the decimal value of the exponent to the nearest whole number. For example, if you need to calculate 1x10^7.2, you can round the exponent to 8 and calculate 1x10^8 instead. This will give you a close approximation of the desired result.
Alternatively, you can use a different calculator or software that does support the use of decimal values in the exponent. This will allow you to calculate the value more accurately.

The EE (or x10^x on Casios) does give a syntax error if you use it with decimal exponents, but the expressions do calculate correctly if you use the full expression with the general power key. The EE key is a shortcut and may have been designed to accept only integer values for the exponents.
I tried that on Casio and the TI calculators.

Use the (-) key (just to the right of the decimal point key) instead of the - key when entering a negative number (not just exponents).
- is used to subtract one value from another. (-) is used to negate a value. - operates on two numbers, (-) operates on one.

I think what you did was use the minus sign instead of the negative sign, on that calculator, the two are not interchangeable. I purposely used the minus sign just now and also got a syntax error, but it looks like it works with the negative sign (-) located under the 3 button.

1. Press [2nd][LN] to activate the exponential function.
2. Type in the exponent 0.2
3. Press [EXE]
   

[2nd][LN]0.2[EXE] Result is 1.221452758

DO NOT PRESS [^] : this is the source of the syntax error.
You can put the exponent in parentheses.
If exponent is negative, press the change sign key (-) right after the e appears on screen.

[2nd][LN][(-)]0.2 [EXE] gives 0.8187307531

I'm assuming the lack of a response means using the proper key did the trick.

Uh yes it will allow you to enter a negative exponent.... press the numbers you want then hit EXP button, then hit the +/- button and then the exponent. 60 % of the time, it works...... everytime.

Hello,
I am no seer, nor will I try to guess what may have happened. This error may come from various conditions
1. The most common reason is an omitted right parenthesis. For instance you press the [sin] function key. It shows as sin( , notice the right parenthesis. You enter the variable, say X, and you press [ENTER]. The calculator gives you a syntax error: It does not know what to do as long as you do not insert the closing parenthesis.
2. Another common source of this error message is the use of the regular MINUS sign instead of the (-). The latter appears on the scren as a smaller, raised minus sign. This is especially true when you want to raise a number or a variable to a negative exponent.

Every function has one way it takes in its food (argument). If you don't do it the right way, it gives you an error. The nice thing is that the calculator gives you the opportunity to correct the error. Whenever you see Error 1:quit 2: Go to, choose GO TO because the calculator shows you exactly the symbol that is creating havoc: It will be highlighted.

Hope it helps.

Hello
To raise a number to any power you use the [^] caret key or on some calculators the [x^y] (x raised to exponent y)

20^(4) =160000

20 to the power of negative 3
20[^] 3 [(-) or +/-] ENTER gives 1.25x10^(-4) = 0.000125 (-) is the small minus sign.

If that gives you a syntax error
20[^] [(-) or +/-] 3[ENTER] = 0.000125

27 [^] (1/3] represents the cube root of 27 which is 3.
Hope it helps.

Hello

To calculate a number to an arbitrary power you use the button labeled ^ .

If you want the cube of 2 your enter
[2][^][3] will give you 8. If your exponent is negative use the sign change key (-) and close the negative exponent between parentheses : for exemple the sequence to compute 2 to power of negative 5 is as follows
2[^] [(] 5 [(-)] [)] which means you enter the value of the exponent before the change sign (-). If you use the big MINUS sign you will get a syntax error.

Hope it helps.