sin50⁰ - sin70⁰+cos80⁰=?

Explanation:

Another Explanation (5): sin50⁰ - sin70⁰ + cos80⁰ = ? আমরা জানি, sinC - sinD = 2cos\(\frac{C+D}{2}\)sin\(\frac{C-D}{2}\) 🤓 তাহলে, sin50⁰ - sin70⁰ = 2cos\(\frac{50+70}{2}\)sin\(\frac{50-70}{2}\) = 2cos\(\frac{120}{2}\)sin\(\frac{-20}{2}\) = 2cos60⁰sin(-10⁰) 😮 = 2 \(\times\) \(\frac{1}{2}\) \(\times\) (-sin10⁰) [যেহেতু cos60⁰ = \(\frac{1}{2}\) এবং sin(-x) = -sinx] = -sin10⁰ 😎 সুতরাং, sin50⁰ - sin70⁰ + cos80⁰ = -sin10⁰ + cos80⁰ = -sin10⁰ + cos(90⁰ - 10⁰) 🤩 = -sin10⁰ + sin10⁰ [যেহেতু cos(90⁰ - θ) = sinθ] = 0 🤗 অতএব, sin50⁰ - sin70⁰ + cos80⁰ = 0 😊