যদি \(sin c=\cfrac{4}{5}\) হয়, তবে \(cos c\times cosec c= -----\)
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\(sin c= \) লম্ব/ অতিভূজ\(=\cfrac{4}{5}\)
ধরি,লম্ব \(=4k\) একক এবং অতিভূজ \(=5k\) একক
\(\because\) ভূমি\(^2\)=অতিভূজ\(^2\)-লম্ব\(^2\)
\(=(5k)^2-(4k)^2 =25k^2-16k^2\)
\(=9k^2\)
∴ভূমি =\(\sqrt{9k^2}=3k\)
\(∴ cos c=\) ভূমি/অতিভূজ \(=\cfrac{3k}{5k}=\cfrac{3}{5}\)
এবং \(cosec c= \) অতিভূজ/লম্ব \(=\cfrac{5k}{4k}=\cfrac{5}{4}\)
\(∴ cos c × cosec c =\cfrac{3}{5}×\cfrac{5}{4}=\cfrac{3}{4}\)
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