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  1. If
    cos α
    = n and
    cos α
    = m , then the vlaue of cos² β is
    sin βcos β
    1. m² + n²
    2. 1
      m² + n²
    3. m² + n²
    4. 0
Correct Option: C

cos α
= n and
cos α
= m
sin βsin β

⇒ cosα = n sinβ and cosα = m cosβ.
∴ n² sin² β = m² cos² β
⇒ n² (1 – cos² β) = m² cos² β
⇒ n² – n² cos² β = m² cos² β ⇒ m² cos² β + n² cos² β = n²
⇒ cos² β (m² + n² ) = n²
⇒ cos²β =
m² + n²



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