allerycos(2θ) can be written as:
A1 − 2 sin²θ
B2 sinθ cosθ
C1 + 2 cos²θ
Dtan²θ − 1
Answer & Solution
Correct answer: A. 1 − 2 sin²θ
1. Three equivalent forms of double-angle cosine:
2. cos 2θ = cos²θ − sin²θ = 1 − 2 sin²θ = 2 cos²θ − 1.
3. Distractor 2 sinθ cosθ is sin 2θ.
_Source: syllabus Maths Ch 3 §3.4 Double Angle Formulas_
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