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Trigonometric identities
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Learn it Key identities: tan θ = sin θ/cos θ and sin²θ + cos²θ = 1 (so 1 − sin²θ = cos²θ). To prove an identity, work on one side only, rewrite in sin and cos, and simplify until it matches the other side.
Example: Simplify (1 − cos²θ)/sin θ.
- 1 − cos²θ = sin²θ.
- sin²θ/sin θ = sin θ.
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