Answer:
(d).
Step-by-step explanation:
sin² β + cos² β = 1
cos (α + β) = cos α cos β - sin α sin β
cos α = √(1 - ) = 21 / 29
cos β = 12 / 13
sin β = √(1 - ) = 5 / 13
sin α = 20 / 29
cos (α + β) = ×
-
×
=
1) The number √ , where n is a prime number is
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