Non-Real ERROR
Casio Casio Calculator
Severity: MinorWhat Does This Error Mean?
Casio Non-Real ERROR means the result of a calculation is a complex (imaginary) number, but the calculator is in real-number mode and cannot display it. Common causes are taking the square root of a negative number (√-4), arcsin or arccos of a value outside -1 to 1, or logarithm of a negative number. Switch to Complex mode on supported models to compute complex results.
Affected Models
- Casio fx-991EX / CW (ClassWiz)
- Casio fx-CG50
- Casio fx-9750GIII
- Casio fx-82ES / MS
- Casio fx-991ES Plus
Common Causes
- Square root of a negative number: √(-4) is 2i in complex numbers but invalid in real mode
- Inverse trig of a value outside the real domain: arcsin(2) has no real solution
- Logarithm of a negative number: ln(-3) is a complex number
- Power of a negative base with a fractional exponent: (-8)^(1/3) treated as complex
- The calculator is in REAL mode and complex results are not permitted
How to Fix It
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Enable Complex mode on supported models.
On Casio fx-991EX / CW: press SETTINGS (SHIFT + SETUP or the menu) → Number Format → Complex Mode → enable. On fx-CG50: go to RUN-MAT mode → SETUP → Complex Mode → set to a+bi or r∠θ. This allows the calculator to return complex results.
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Check the input value is in the valid real domain.
For √x: x must be ≥ 0. For arcsin(x) and arccos(x): x must be between -1 and 1. For arctan(x): any real value works. For log(x): x must be > 0. If your input is outside these ranges, the result is complex.
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Use the absolute value to take the root of a negative number in real mode.
If you need the real cube root of a negative number (e.g. the real solution of ³√(-8) = -2), use the formula -((|x|)^(1/3)) manually, since the calculator may not evaluate this automatically in real mode.
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Check the preceding calculation that produced the input.
If the Non-Real ERROR occurs in the middle of a multi-step calculation, an intermediate result may have gone negative unexpectedly. Break the calculation into steps and check each intermediate result.
Frequently Asked Questions
Which Casio models support complex number calculations?
The Casio fx-991EX (ClassWiz), fx-CG50, fx-9750GIII, and fx-9860GII support complex number mode. Most scientific calculators in the fx-82, fx-85, and fx-100 series do not support complex mode and will always show Non-Real ERROR for complex results.
Is Non-Real ERROR the same as MATH ERROR on older Casio models?
Similar but not identical. MATH ERROR covers domain errors (including complex results) on older models, while newer Casio calculators with complex mode distinguish between a MATH ERROR (undefined operation) and a Non-Real ERROR (valid operation but complex result).