The single most common source of lost marks in trig - your answer is only correct if the angle mode matches the question. AA usually uses radians; AI usually uses degrees.
In short: Degrees and radians are two angle modes, and every trigonometric calculation depends on which one the calculator is in. Check the mode in the settings before any sin, cos or tan question: use radians when angles are given in terms of π or as arc lengths, and degrees when they are given in degrees.
| TI-84 Plus CE | Casio fx-CG50 and fx-CG100 | TI-Nspire CX | |
|---|---|---|---|
| Key sequence | Press MODE, highlight RADIAN or DEGREE on the angle row and press ENTER, then 2nd → MODE to quit. | Press SHIFT → MENU (SET UP) → Angle, then choose Deg or Rad and EXIT. | Press ctrl → menu → Settings (or doc Settings) → Angle, and choose Degree or Radian. |
Tip: If a sin/cos/tan answer looks wildly wrong, the angle mode is almost always the cause.
Tip: If a sin/cos/tan answer looks wildly wrong, the angle mode is almost always the cause.
Tip: If a sin/cos/tan answer looks wildly wrong, the angle mode is almost always the cause.
Here's a real IB-style question that uses exactly this technique.
Given θ = π/6 radians, find sin θ. Give your answer as an exact value.
The single most common source of lost marks in trig - your answer is only correct if the angle mode matches the question. AA usually uses radians; AI usually uses degrees. A question gives an angle in radians (often containing π) - common in AA calculus and trig. A question gives an angle in degrees, e.g. a bearing or a real-world angle - common in AI.
1. Check the question: are angles in degrees (°) or radians (π, rad)? 2. Press MODE, highlight RADIAN or DEGREE on the angle row and press ENTER, then 2nd → MODE to quit. 3. Re-enter the calculation after switching - the mode only affects new work.
1. Check the question: are angles in degrees (°) or radians (π, rad)? 2. Press SHIFT → MENU (SET UP) → Angle, then choose Deg or Rad and EXIT. 3. Re-enter the calculation after switching - the mode only affects new work.
1. Check the question: are angles in degrees (°) or radians (π, rad)? 2. Press ctrl → menu → Settings (or doc Settings) → Angle, and choose Degree or Radian. 3. Re-enter the calculation after switching - the mode only affects new work.
If a sin/cos/tan answer looks wildly wrong, the angle mode is almost always the cause.
In the worked example on this page (2 marks, Paper 1), the marks are: M1: Correct mode: radians; A1: 1/2.
Questions that need this technique link back to this guide. Try one in practice mode, or see every GDC guide.