Introduction to Trigonometry · Mathematics, chapter 8

Read the section map, ask questions about this chapter, run the concept animations, then take a quiz and see which sections to go back to.

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Trigonometric ratios on the unit circle

conceptId: trig-unit-circle

Trigonometric ratios on the unit circle

CBSE Class 10 Mathematics · Ch 8 §8.2 — the radius is 1, so the coordinates of P are (cos θ, sin θ).

sin θ
0.574
cos θ
0.819
tan θ = sin θ / cos θ
0.700
sin²θ + cos²θ
1.000000

What to notice: sin θ and cos θ are just the legs of a right triangle drawn inside a circle of radius 1 — as θ sweeps, sin θ rises to 1 at 90° and falls back, while cos θ does the opposite, and sin²θ + cos²θ stays pinned at 1.

Try this: set θ = 90° and read tan θ — cos θ is 0 there, so the ratio is undefined. Then try θ = 45° and compare sin θ with cos θ.

10 further animations in the registries belong to other chapters.

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