cos(120° +A)+ cos(120°-A) =?

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 🥳