is equal to

Question

is equal to

Canvas Classes · Accepted Answer

🧠 Doubling-Angles Cosine Product = Telescope

Look at the angles in the product: . Each angle is double the previous. That is the signal for the famous telescoping identity:

.

The proof in one line: multiply and divide by . Then , and , and so on — each step doubles the sine. After  doublings, we get  in the numerator and  in the denominator.

This identity is JEE bread-and-butter. Anytime you see a product where each cosine angle is double the previous, this is the formula to use.

🗺️ Worki

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