What you'll learn

31 lessons in Trigonometry

Right-triangle trig (SOHCAHTOA)The unit circleGraphs of sin and cosTrig identitiesLaw of sinesLaw of cosinesInverse trig & their domainsSum & difference formulasDouble-angle & half-angle formulasGraphs of tan, sec, csc, cotSolving trig equationsArea of triangle via trigTrig form of complex numbersDe Moivre's theoremRoots of unityProving trig identitiesLimit $\sin x / x \to 1$ (geometric proof)Spherical trigonometry previewHyperbolic functionsPolar curvesSolving triangles: law of tangents & half-angleTrigonometric series & Gregory's formula for πSpherical trigonometryProduct-to-sum & sum-to-productHarmonic addition: a·sin + b·cosThe tangent half-angle substitutionChebyshev polynomialsEuler's formula & trig identitiesPower-reduction & multiple-angle expansionSimple harmonic motion & sinusoidal modelingFourier series (introduction)

How Erudia teaches

Built to be understood — and remembered.

Every idea is taught with motivation and a worked example before the drills, and an FSRS spaced-repetition engine schedules each review for the moment just before you'd forget it. A short placement check finds what you already know, so you start Trigonometry exactly where it's useful.

Start Trigonometry →