Use the result cosx*cos(60-x)*cos(60+x)=1/4 cos 3x (Question: 108045.0 )

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Samresh

· started a discussion

· 1 Months ago

Use the result cosxcos(60-x)cos(60+x)=1/4 cos 3x (Question: 108045.0 )

Using the above mentioned formula,we have x=20, 60-x=40 and 60+x=80
So, this will give 1/4 cos 3*20= 1/4 cos 60
Thus we can write :
cos 20*cos40*cos60*cos80= 1/4 cos 60 * cos 60
= 1/4 *1/2 *1/2 =1/16 .

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 20^o cos 40^o). cos80^o . cos60^o

Deeksha Singhal

· commented

· 1 Months ago

really good

Ravi Shankar Gupta

· commented

· 1 Months ago

nice

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