Radians & Degrees on TI-84 — Switch Modes and Convert

Wrong angle mode is the #1 cause of wrong answers on trig exams. The math is right, the keystrokes are right — but the calculator is interpreting your angles in the wrong unit, and every answer comes out garbage. This guide shows how to switch modes, how to check the current mode in two seconds, and how to override the mode for a single calculation.

Why it matters: one keystroke, two answers

Compute sin(30) in each mode:

Mode	`sin(30)` returns	Interpretation
Degree	`0.5`	sin of 30 degrees ✓
Radian	`-0.9880316241`	sin of 30 radians (about 1718°)

If you expected 0.5 and got −0.988, nothing is broken — the calculator is in radian mode. This single mismatch has sunk countless exam questions.

How to switch modes

Press MODE
Arrow down to the third line, which shows RADIAN DEGREE
Arrow to highlight the one you want and press ENTER — the highlight must actually move onto your choice and you must press ENTER to lock it in
Press 2nd MODE (QUIT) to return to the home screen

The setting persists until you change it again — even through power off. That's exactly why it bites people: last week's physics homework leaves the calculator in degrees, and today's calculus quiz needs radians.

How to check the current mode instantly

Method 1 — the MODE screen. Press MODE and look at the third line; the highlighted word is the active setting. Fastest and unambiguous.

Method 2 — the sin(180) test. From the home screen, compute sin(180):

sin(180)
        0            ← degree mode (sin 180° = 0)
sin(180)
        -.8011526357 ← radian mode (180 rad is not a special angle)

A clean 0 means degree mode; roughly −0.80 means radian mode. Make this a reflex at the start of any trig-heavy test.

Angle overrides: force a unit for one calculation

You can tag any angle with an explicit unit that overrides the mode setting, using the ANGLE menu at 2nd APPS:

Menu item	Symbol	Effect
`1: °`	degree symbol	Treats the number as degrees, even in radian mode
`3: r`	radian symbol	Treats the number as radians, even in degree mode
`4: ►DMS`		Converts decimal degrees to degrees-minutes-seconds

Example — degrees while in radian mode:

sin(30°)
        .5

Keystrokes: SIN 3 0, then 2nd APPS 1 to paste the ° symbol, ) ENTER. Correct answer, mode untouched — ideal when a calculus test (radian mode) throws in one degree-based question.

Example — ►DMS conversion: in degree mode, compute 54.34►DMS (paste ►DMS from 2nd APPS 4):

54.34►DMS
        54°20'24"

Manual conversion formulas

Conversion	Multiply by	Example
degrees → radians	π/180	45 × π/180 = 0.7853981634 (= π/4)
radians → degrees	180/π	(π/3) × 180/π = 60

On the calculator: 45 × 2nd ^ (π) ÷ 180 ENTER gives .7853981634. These two formulas also let you sanity-check any suspicious answer.

Which mode for which course?

Course / test	Mode	Why
Geometry	Degree	All angle measures are in degrees
Physics	Degree (usually)	Projectile angles, forces, and vectors are stated in degrees
Precalculus (unit circle)	Radian	Unit-circle values like π/6, π/4, π/3
Calculus (AP Calc AB/BC)	Radian	Derivative rules like d/dx sin x = cos x are only true in radians
SAT	Depends on the problem	Match the units in the question — degrees for a "30° angle," radians when the problem uses π. Check before each trig question

Rule of thumb: if the problem contains a ° symbol, use degrees; if it contains π in the angle, use radians.

Quick self-check routine before any trig test

Press MODE — confirm the third line matches the course
Compute sin(180) — expect 0 in degree mode
If a single question uses the other unit, use the 2nd APPS override rather than flipping modes back and forth

Note: simple scientific calculators handle this too — the online TI-30XS has its own DEG/RAD mode with the same failure pattern, so the habit transfers.

Practice right now

Open the free online TI-84 calculator — a full TI-84 Plus CE in your browser, no download needed — and run the drill: switch to radian mode, verify sin(30) gives −0.988, then compute sin(30°) with the ANGLE override and watch it return 0.5. Once you've seen the wrong answer on purpose, you'll recognize it instantly on exam day.