Explanation: 
Another Explanation (5):
cos(120° + A) + cos(120° - A) এর মান নির্ণয়:
আমরা জানি, cos(C + D) + cos(C - D) = 2cosCcosD 🤓
এখানে, C = 120° এবং D = A
সুতরাং, cos(120° + A) + cos(120° - A) = 2cos(120°)cos(A) 🤔
এখন, cos(120°) = cos(180° - 60°) = -cos(60°) = -\(\frac{1}{2}\) 🤯
অতএব, 2cos(120°)cos(A) = 2 \(\times\) (-\(\frac{1}{2}\)) \(\times\) cos(A) = -cos(A) 🎉
সুতরাং, cos(120° + A) + cos(120° - A) = -cosA 🥳
