Question Detail
Question
The exact value of cos35° cos25° - sin35° sin25°
Correct Answer
Option A is the correct answer.
Detailed Explanation
Using cosine addition formula: cos(A+B) = cosA cosB - sinA sinB. Here A=35°, B=25°, so cos35° cos25° - sin35° sin25° = cos(35°+25°) = cos60° = 1/2.
Hint
Recognize the cosine addition formula.