sin²18°+sin²36°+sin²54°+sin²72° =  কত ?  

Explanation:

Another Explanation (5): bài giải : \( \begin{aligned} & \sin^2 18^\circ + \sin^2 36^\circ + \sin^2 54^\circ + \sin^2 72^\circ \\ &= \sin^2 18^\circ + \sin^2 36^\circ + \sin^2 (90^\circ - 36^\circ) + \sin^2 (90^\circ - 18^\circ) \\ &= \sin^2 18^\circ + \sin^2 36^\circ + \cos^2 36^\circ + \cos^2 18^\circ \\ &= (\sin^2 18^\circ + \cos^2 18^\circ) + (\sin^2 36^\circ + \cos^2 36^\circ) \\ &= 1 + 1 \\ &= 2 \end{aligned} \)
অতএব, sin²18°+sin²36°+sin²54°+sin²72° = 2 🥳