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Which one of these is NOT equal to cos 2A?
A2 cos²A − 1
B2 sin²A − 1
C1 − 2 sin²A
Dcos²A − sin²A
Answer & Solution
Correct answer: B. 2 sin²A − 1
The three correct forms of cos 2A are cos²A − sin²A, 2cos²A − 1 and 1 − 2sin²A; the first option has the wrong sign.
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