When do I use sin²θ + cos²θ = 1 in Trigonometry, and what does it mean?
the fundamental Pythagorean identity.
sin²θ + cos²θ = 1 — the fundamental Pythagorean identity. Use it when: any real angle θ. Always check the condition holds before plugging in numbers.
Key point
sin²θ + cos²θ = 1
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