TI-84 and TI-Nspire mistakes in IB Maths exams, and the settings that prevent them

The best TI-84 and TI-Nspire tips for IB exams are about settings and habits, not buttons: check radian or degree mode before every trig question, keep full precision until the final answer, widen the graph window until you have every solution, include the frequency list in statistics, enter σ rather than σ², and write the maths rather than the keystrokes. Below, each mistake comes with its fix for the TI-84 Plus CE and the TI-Nspire CX (non-CAS). The ideas transfer to Casio, NumWorks and HP models; only the menus differ.

The calculator matters on every paper except AA Paper 1, which is calculator-free (see our AA Paper 1 guide for that one). On AI, it is needed on every paper.

Which calculators are allowed, and what is exam mode?

From the IB's 2026 calculator rules:

• TI-84 (all models) and TI-83 Plus are allowed. TI-83/84 users do not use the built-in test mode, because it blocks apps the IB permits (such as the polynomial and simultaneous-equation solver). Instead, RAM and archive are reset and non-approved apps removed.
• TI-Nspire CX and CX II (non-CAS) are allowed on OS 5.4 or later, in Press-to-Test with the specified features blocked.
• TI-Nspire CX II CAS models are allowed only with CAS disabled in Press-to-Test. CAS (symbolic algebra) is not permitted in IB maths exams.
• Casio models such as the fx-CG50, fx-9750GIII and fx-9860GIII, NumWorks and HP Prime are allowed when updated and in their IB exam mode.
• Not allowed: TI-89, TI Voyage 200, older Nspire CAS models, Casio ClassPad and fx-CG500, HP 38–95, and anything with student-accessible Wi-Fi. Phones and calculator apps don't count.

Exam mode has to be switched on immediately before the exam and stay on throughout. Your school's exams team runs this, so follow their instructions.

Radians or degrees: how do you avoid the wrong mode?

The wrong angle mode produces answers that look plausible, which is why it survives to the end of the paper.

• sin 30 in degree mode is 0.5. In radian mode it is −0.988.
• ∫₀¹ sin x dx is 1 − cos 1 = 0.460. In degree mode the calculator integrates sin of 1 degree, not 1 radian, and returns 0.00873.

The rule: degrees when the question gives or asks for angles in degrees (triangles, bearings, most AI geometry). Radians when π appears, for arcs and sectors measured in radians, and always for calculus with trig functions.

• TI-84 Plus CE: press mode and select RADIAN or DEGREE on the angle line. The mode is shown in the status bar at the top of the screen; glance at it before every trig question.
• TI-Nspire CX: the angle setting is under Document Settings (or Settings from the home screen). The status bar shows RAD or DEG for the current document.

A useful check: if your answer to an angle question is negative, larger than 180°, or tiny when it shouldn't be, check the mode before anything else.

Why does rounding too early cost marks?

On calculator papers the IB accepts the exact answer or the answer correct to 3 significant figures. That applies to the final answer. Round in the middle and the error travels.

Example: bacteria double every 5.7 hours, so N = 400e^kt with k = ln 2 / 5.7. Find N after 48 hours.

Only the first is correct. Rounding k to three significant figures, which feels safe, already changes the answer.

Store values instead of retyping them

• TI-84 Plus CE: after calculating, press sto→, then alpha and a letter (for example alpha math for A), then enter. Use the stored letter later. The previous answer is always available as Ans (2nd (−)).
• TI-Nspire CX: type k:=ln(2)/5.7, or use ctrl var (sto→) after a result. Stored variables are listed under the var key.

Float, fix and exact output

If your TI-84 is set to FIX 2 in the mode screen, every value is displayed to 2 decimal places, and you may copy those into later steps. Keep it on FLOAT. On the Nspire, Display Digits sets the same thing, and in Auto mode it may show an exact fraction or surd; press ctrl enter for a decimal.

Why did the graph miss an intersection?

Solve 2^x = x². On a standard window (x and y from −10 to 10) you see two intersections, at x ≈ −0.767 and x = 2. There is a third at x = 4, where y = 16, above the top of the window.

Habits that stop this:

• Zoom to fit, then adjust. TI-84: zoom then ZoomFit (option 0) rescales y for your x range; set x yourself under window. Nspire: menu → Window/Zoom → Zoom – Fit, or Window Settings.
• Think about the functions. 2^x eventually grows faster than x², so after the second crossing they must cross again. A quick check of end behaviour tells you how many solutions to expect.
• Respect the domain in the question. If it says 0 ≤ x ≤ 2π, set the window to exactly that and count the crossings.
• Use the built-in tools, not tracing. TI-84: 2nd trace (CALC) → intersect, then select the two curves and give a guess near the crossing. Nspire: menu → Analyze Graph → Intersection, then set the lower and upper bounds. Tracing gives an approximate pixel position, not a 3 s.f. answer.

How do you use the solver and numerical calculus safely?

Solvers find one root at a time

x³ = 2x + 1 has three solutions: x = −1, x ≈ −0.618 and x ≈ 1.62. A numerical solver (TI-84: Solver in the math menu; Nspire: nSolve, under menu → Algebra) returns one root, usually one near your starting guess. Graph first to count roots, then solve once per root with a guess near each. For polynomials, the TI-84 PlySmlt2 app (under apps) and the Nspire's polynomial tools (under menu → Algebra) give all the roots at once.

Numerical derivatives can lie

The numerical derivative (TI-84: nDeriv( in the math menu; Nspire: menu → Calculus → Numerical Derivative at a Point) estimates the gradient from points either side. For y = |x| at x = 0 it returns 0, even though the derivative does not exist there. Use it to check a gradient you found by hand or to find a gradient at a smooth point, not to decide whether a function is differentiable.

Numerical integrals: write the integral down

fnInt( on the TI-84 (also in the math menu) and Numerical Integral on the Nspire give definite integrals quickly. For an area between a curve and the x-axis where the curve dips below the axis, integrate the absolute value, or split at the root; a plain integral counts the area below as negative. Always write the integral with limits on the page before the answer.

Why are my statistics wrong when the data is right?

The frequency column

Scores 1 to 5 with frequencies 3, 7, 9, 6, 5. Run one-variable stats on the scores alone and you get a mean of 3 from n = 5. With the frequencies included, the mean is 93/30 = 3.1 from n = 30.

• TI-84 Plus CE: stat → Edit to enter scores in L1 and frequencies in L2, then stat → CALC → 1-Var Stats with List: L1 and FreqList: L2.
• TI-Nspire CX: enter the data in named columns in Lists & Spreadsheet, then menu → Statistics → Stat Calculations → One-Variable Statistics, and choose the frequency column in the Frequency List field.

Check n in the output every time. If n is not the total frequency, the frequency list is missing.

The output shows two standard deviations: σx divides by n, Sx (sx on the Nspire) divides by n − 1. They differ noticeably for small samples. Check in your notes which one your course uses for describing a data set and which for estimating a population (an AI HL topic), and don't copy whichever appears first.

Regressions: x and y the right way round, r not r²

• Lists in the right order. The first list is the independent variable. Swapping them gives a different line, not just a different label.
• Turn diagnostics on (TI-84). Without it, LinReg doesn't show r or r². On the Plus CE, set STAT DIAGNOSTICS to ON in the mode screen; on older models run DiagnosticOn from the catalog (2nd 0). The Nspire shows both by default.
• r is not r². If a question asks for Pearson's correlation coefficient, give r with its sign. r² = 0.884 could be r = 0.940 or r = −0.940, and taking the square root loses the sign.
• Know the output form. The calculator's exponential regression is y = a·b^x. If the question wants y = Ae^kx, then A = a and k = ln b.

Normal distribution: σ or σ², and which tail?

IB notation is X ~ N(μ, σ²): the second number is the variance. Calculators want the standard deviation. For X ~ N(50, 16), enter σ = 4. Using 16 turns P(X < 54) = 0.841 into 0.599.

• TI-84 Plus CE: 2nd vars (DISTR) → normalcdf(lower, upper, μ, σ). For "less than 54", use a very large negative lower bound such as −1E99 (the EE key is 2nd ,).
• TI-Nspire CX: menu → Statistics → Distributions → Normal Cdf, with −∞ or −9E999 as the lower bound.

Inverse normal: which tail?

Inverse normal works from the area to the left by default. Heights are N(170, 8²) and you want the height that only the tallest 10% exceed: the area to the left is 0.9, so the answer is invNorm(0.9, 170, 8) = 180 cm (180.25). Entering 0.1 gives 160 cm (159.75), the cut-off for the shortest 10%. Some calculators let you choose a tail (left, right or centre); if yours does, check which one is selected before you trust the answer.

Sketch the bell curve and shade the region before you press anything. It takes five seconds and catches most tail mistakes.

Finance (AI): why does the TVM solver give a negative answer?

TVM solvers (TI-84: apps → Finance → TVM Solver; Nspire: menu → Finance → Finance Solver) use a sign convention: money you pay out is negative, money you receive is positive.

Common slips: N entered as years (6) instead of the number of payment periods (72) when P/Y is 12; I% entered as 0.035 instead of 3.5; and P/Y or C/Y left at a previous value. A negative FV for an investment means you entered PV as positive; report the amount as positive in words ("the investment is worth 6166.51"). On the TI-84, place the cursor on the unknown and press alpha enter to solve.

How should you write calculator work so it still earns method marks?

Examiners mark mathematics, not keystrokes. Write the setup in standard notation, then the result.

• Write what you solved. The equation, the integral with its limits, the distribution with its parameters, the regression type. These carry the method marks if the final number is wrong.
• Write the intermediate values to more than 3 s.f. if a later part depends on them, and say you're using the stored value.
• Sketch when you used a graph. A labelled sketch showing the intersection you found is quick working for a "solve" question.
• Give the final answer to 3 s.f. or exact, unless the question asks for something else (a whole number of people, money to 2 decimal places, an angle to 1 decimal place).

Calculator slips sit alongside the algebra and reading mistakes covered in our Maths AA common mistakes and Maths AI common mistakes guides. On AI HL, they matter most on the long modelling questions; see our AI HL Paper 3 guide for a worked example.