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Ravi Raj Meena

· started a discussion

· 1 Months ago

IF 4θ

Question:
Find the value of cos20° cos40° cos60° cos80°.
Options:
A) \(\cfrac{1}{16}\)
B) \(\cfrac{3}{16}\)
C) 1
D) 0
Solution:
Ans: (a)

cos20° cos40° cos60° cos80° = cos20° cos40° cos80°.cos60°

\(\cfrac{1}{2}\) (2cos 20o  cos 40o). cos80o . cos60o


arunesh

· commented

· 1 Months ago

cos@cos(60-@)cos(60+@)=1/4cos3@
so cos20cos40cos80=1/4cos60
so overall 1/4*!/2*1/2=1/16

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