Formatted Options:
A. sin²A−cos²A
B. sin²A+cos²A
C. cos²A−sin²A
D. cosA−sinA
Answer:
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
