Trigonometry Playground
Sin, cos and tan are easy to memorise and hard to feel. These demos let you grab the maths and move it around — so the ideas finally click. Built for teens (about 13+), works on any phone.
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Sin, Cos & Tan
The unit circle & waves
Drag an angle around a circle and watch sine, cosine and tangent change in real time. Then see how that spinning point draws a sine wave.
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Solve triangles
The Sine Rule
a/sin A = b/sin B = c/sin C
Drag any corner of a triangle and watch the three ratios stay exactly equal — they even equal the diameter of the circle through all three corners. Plus when to use it.
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Solve triangles
The Cosine Rule
c² = a² + b² − 2ab·cos C
See the formula balance as you reshape a triangle — and watch it turn into Pythagoras the moment the angle hits 90°. Plus when to reach for it.
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Senior years
Radians & Sine Graphs
y = A sin(B(x − C))
Why radians beat degrees — an angle as a distance walked around the circle. Then shape the sine wave with amplitude, period and phase sliders while the circle draws it live.
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Senior years
Trig Identities
sin²+cos²=1 · sin(a+b)
Watch sin²θ + cos²θ stay pinned at exactly 1 while you drag the angle — it's just Pythagoras — then verify the addition formulas live for any pair of angles.
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