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0 votes
11.8k views
in Mathematics by (75.1k points)

If K[sin18° + cos36°] = 5 then K = _________

(a) 2√5

(b) (√5/2)

(c) 4 

(d) 5

1 Answer

+1 vote
by (71.7k points)
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Best answer

The correct option (a) 2√5   

Explanation:

K[sin18° + cos36°] = 5

∴ sin18 = [(√5 – 1)/4] and cos36 = [(√5 + 1)/4]

∴ K[{(√5 – 1)/4} + {(√5 + 1)/4}] = 5

∴ K(√5/2) = 5

∴ K = 2√5.

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