Q.If \(\cos \theta + \sec \theta = 2\), find the value of \(\cos^9 \theta + \sec^9 \theta\).

Given: \(\cos \theta + \sec \theta = 2\) Or, \(\cos \theta + \cfrac{1}{\cos \theta} = 2\) Or, \(\cfrac{\cos^2 \theta + 1}{\cos \theta} = 2\) Or, \(\cos^2 \theta + 1 = 2 \cos \theta\) Or, \(\cos^2 \theta + 1 - 2 \cos \theta = 0\) Or, \((\cos \theta - 1)^2 = 0\) ⇒ \(\cos \theta - 1 = 0\) ⇒ \(\cos \theta = 1\) Therefore, \(\cos^9 \theta + \sec^9 \theta\) \(= \cos^9 \theta + \cfrac{1}{\cos^9 \theta}\) \(= (1)^9 + \cfrac{1}{(1)^9}\) \(= 1 + 1\) \(= 2\) (Answer)
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