alleryFor all real x, the value of sin²x + cos²x is:
A0
B-1
C2
D1
Answer & Solution
Correct answer: D. 1
Pythagoras applied to the unit circle: if P(a, b) is on the unit circle with cos x = a and sin x = b
then a² + b² = 1, hence cos²x + sin²x = 1 for all x ∈ ℝ.
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