যদি \(3x=cosecα \) এবং \(\cfrac{3}{x} = cot α\) হয়, তাহলে \(3(x^2-\cfrac{1}{x^2}) \) -এর মান (a) \(\cfrac{1}{27}\) (b) \(\cfrac{1}{81}\) (c) \(\cfrac{1}{3}\) (d) \(\cfrac{1}{9}\)

Answer: C
\(3x+\cfrac{3}{x}=cosecα+cotα \)
বা, \(3(x+\cfrac{1}{x})=cosceα+cotα \)

আবার, \(3x-\cfrac{3}{x}=cosecα-cotα \)
বা, \(3(x-\cfrac{1}{x})=cosceα-cotα\)

\(∴3(x+\cfrac{1}{x})×3(x-\cfrac{1}{x})\)
\(=(cosceα+cotα )(cosceα-cotα)\)
বা, \(3×3\left(x^2-\cfrac{1}{x^2} \right)=cosec^2 α-cot^2⁡α \)
বা, \(3×3\left(x^2-\cfrac{1}{x^2}\right)=1 \)
বা, \(3\left(x^2-\cfrac{1}{x^2} \right)=\cfrac{1}{3} \)

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