Which calculator?
The computer-based tests only allow non-programmable scientific calculators. The Casio ClassWiz range is the usual choice. Check your module’s rules, but the fx-991 models are the ones worth having, because they do matrices, simultaneous equations and complex numbers. The cheaper fx-83 and fx-85 don’t.
There are two generations, with different menus (exact key names can vary slightly between versions, so check against your own):
- fx-991EX (older): press MENU, then a number or letter for each mode.
- fx-991CW (newer): press HOME and pick an app with the arrow keys.
Determinants and matrix maths
Used in Matrices and Cramer’s rule and Mesh analysis.
| Step | fx-991EX | fx-991CW |
|---|---|---|
| Open | MENU → 4 (Matrix) | HOME → Matrix |
| Define a matrix | Choose MatA, set rows and columns, type the values (= after each) | TOOLS → define MatA, set size, type the values |
| Back to calculate | AC | AC |
| Determinant | OPTN → Determinant → OPTN → MatA → ) → = | CATALOG → Matrix → Matrix Calculation → Det → MatA → ) → EXE |
| Inverse | MatA then x⁻¹ | MatA then x⁻¹ |
Simultaneous equations
The fastest way to solve a 3×3 mesh matrix (show working separately if the question asks for it).
| Step | fx-991EX | fx-991CW |
|---|---|---|
| Open | MENU → A (Equation/Func) → 1 (Simul Equation) → 3 unknowns | HOME → Equation → Simul Equation → 3 unknowns |
| Enter | Type each row’s coefficients, then the constant | Same |
| Solve | = and step through , , | EXE and step through |
Check: for the system in the Mesh analysis worked example, you should get 4.457, 3.429 and 3.943.
Complex numbers
Needed later for AC impedance ().
- fx-991EX: MENU → 2 (Complex). The imaginary unit is ENG. Convert to polar with OPTN → ▶r∠θ.
- fx-991CW: HOME → Complex. Same idea through the TOOLS or OPTN menu.
Engineers write for ; the calculator writes . They’re the same.
Repeating a calculation with different values
For tables like RC charging at 0.1τ, 0.5τ, 1τ…: type the full expression once, press =, then use the left arrow to go back into it, change only the value, and press = again. Or use the Table mode with set to your formula.
Solving any one equation (SOLVE)
Type the equation using the variable (ALPHA then the X key), e.g. 5(1-e^(-X/0.47))=4, then SHIFT → SOLVE (fx-991EX) or the equivalent in the Calculate app’s TOOLS menu on the CW. It finds numerically, which is handy when you can’t rearrange easily.
Habits that save marks
- Check degrees or radians (shown at the top of the screen) before any trig. Kinematics usually needs radians.
- Use the ×10ˣ key for engineering powers:
470×10^-6for 470 µF. - Store intermediate answers (STO → A) instead of retyping rounded numbers.
- Keep at least 4 significant figures until the final answer.