\(cos^2θ−sin^2θ=\cfrac{1}{x},(x>1)\) হলে, \(cos^4θ−sin^4θ\) = —— ।
Madhyamik 2017
\(cos^2θ−sin^2θ=\cfrac{1}{x},(x>1)\) হলে, \(cos^4θ\) \(−sin^4θ\) = \(\cfrac{1}{x}\)
\(cos^4θ−sin^4θ\)
\(=(cos^2θ−sin^2θ)(cos^2θ+sin^2θ)\)
\(=\cfrac{1}{x}\times 1\, [\because cos^2θ+sin^2θ=1]\)
\(=\cfrac{1}{x}\)