Cos2A is equivalent to: A. sin2A−cos2A B. sin2A+cos2A C. cos2A−sin2A D. cosA−sinA

Formatted Options:

A. sin²A−cos²A

B. sin²A+cos²A

C. cos²A−sin²A

D. cosA−sinA

C. cos²A−sin²A

Step-by-step explanation:

From the double angle formulas, we know that:

cos (A + B) = cosAcosB - sinAsinB

So, if B = A, then the above equation becomes;

cos(A + A) = cosAcosA - sinAsinA      [i.e replacing B with A]

=>cos(2A) = (cosA)² - (sinA)²

=> cos(2A) = cos²A - sin²A

Therefore,

cos(2A) is equivalent to cos²A - sin²A

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step-by-step explanation: