Trigonometry Identities

Trigonometry, clear and in your pocket.

Trigonometry Identities brings together every formula you need for high school, college prep and university (calculus, physics, engineering), with interactive tools that help you actually understand them.

▸ EVERY IDENTITY
• Pythagorean and reciprocal
• Sum and difference of angles
• Complementary, supplementary and opposite angles
• Double, triple and half angle
• Power reduction
• Sum-to-product and product-to-sum
• Law of sines and law of cosines
Crisp formulas, with search and favorites. Long-press any formula to copy it as LaTeX.

▸ INTERACTIVE UNIT CIRCLE
Drag the angle and watch sine, cosine and tangent update live. It snaps to the special angles (30°, 45°, 60°…) and shows the exact value, like √3/2, plus the angle in radians.

▸ SOLVE TRIANGLES STEP BY STEP
Enter any 3 values and get the sides, angles, area and perimeter, with the working and a drawing to scale. It handles the ambiguous case too: when two triangles are possible, it shows both.

▸ IDENTITY LAB
Is sin 2x equal to 2·sin x·cos x? Type both expressions: the app tells you whether they are an identity and plots both graphs so you can see why.

▸ DARK MODE, WORKS OFFLINE
No internet needed. In English and Spanish (follows your phone's language).

Great for high school, SAT/ACT prep, calculus and physics students.
No ads. No sign-up.

Recent changes:
New: AI tutor ✨
• Tap ✨ on any formula for a free step-by-step explanation
• In the Lab: ask for a proof or explanation (3 free a day)
• Optional subscription for unlimited proofs
• In-app notice when a new version is out