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cos 10 cos 50 cos 60 cos 70 = root of 3/16
{ all values of cos are in degrees.}

Asked by Simran Agarwal(student) , on 5/2/13

Answers

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=cos10 cos50 cos60 cos70

=1/2 cos50 cos10 cos70

=1/2 cos(60-Q) cosQ cos(60+Q)               [Q=10;  cos(60-Q) cosQ cos(60+Q)=1/4COS3Q]

=1/2  1/4cos3.10

=1/2 1/4.root of 3/2

=root of 3/16

Posted by Rajan Sajani(student)on 6/2/13

EXPERT ANSWER

We have to evaluate-

=cos10 cos50 cos60 cos70

= cos50 cos10 cos70

The above expression can be manipulated as-

= cos(60-Q) cosQ cos(60+Q)

where, Q=10 such that

cos(60-Q) cosQ cos(60+Q)=

So,

= cos30

Posted by Ayush Jha(MeritNation Expert)on 6/2/13

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