alleryThe fundamental Pythagorean identity in trigonometry is:
A$\sin^2\theta + \cos^2\theta = 1$
B$\tan^2\theta + \cot^2\theta = 1$
C$\sin\theta + \cos\theta = 1$
D$\sin\theta \cos\theta = 1$
Answer & Solution
Correct answer: A. $\sin^2\theta + \cos^2\theta = 1$
**The fundamental Pythagorean identity:** sin²θ + cos²θ = 1 (from x² + y² = 1 on unit circle).
**Other forms:** 1 + tan²θ = sec²θ; 1 + cot²θ = cosec²θ.
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