cos15° এর মান কোনটি?

Explanation:

Another Explanation (5): ```html cos 15° এর মান নির্ণয়: আমরা জানি, cos (A - B) = cos A cos B + sin A sin B ধরি, A = 45° এবং B = 30° তাহলে, cos 15° = cos (45° - 30°) = cos 45° cos 30° + sin 45° sin 30° আমরা জানি, cos 45° = \(\frac{1}{\sqrt{2}}\) 🤩 cos 30° = \(\frac{\sqrt{3}}{2}\) sin 45° = \(\frac{1}{\sqrt{2}}\) sin 30° = \(\frac{1}{2}\) সুতরাং, cos 15° = \(\frac{1}{\sqrt{2}} \cdot \frac{\sqrt{3}}{2} + \frac{1}{\sqrt{2}} \cdot \frac{1}{2}\) = \(\frac{\sqrt{3}}{2\sqrt{2}} + \frac{1}{2\sqrt{2}}\) = \(\frac{\sqrt{3} + 1}{2\sqrt{2}}\) 🥰 অতএব, cos 15° = \(\frac{\sqrt{3} + 1}{2\sqrt{2}}\) 🎉 ```