Another Explanation (5): প্রশ্ন: \(\theta = (2n+1)\pi, \quad n \in \mathbb{Z}\) হবে কখন?
উত্তর: যখন \(\cos \theta = -1\)
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সমাধান:
দেওয়া: \(\theta = (2n+1)\pi, \quad n \in \mathbb{Z}\)
তাহলে, \(\cos \theta = \cos((2n+1)\pi)\)
জানা: \(\cos((2n+1)\pi) = -1\)
অর্থাৎ, \(\cos \theta = -1\)
অতএব, \(\theta = (2n+1)\pi, \quad n \in \mathbb{Z}\) হলে, \(\cos \theta = -1\)
**উত্তর:** \(\boxed{\cos \theta = -1}\)