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Q.

What will be the value of x   in cos2x=cos 60 ° cos 30 ° +sin 60 ° sin 30 °  ?


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a

16 °  

b

15 °  

c

25 °  

d

18 °   

answer is B.

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Detailed Solution

Given that,
cos2x=cos 60 ° cos 30 ° +sin 60 ° sin 30 °   Then on substituting the values of the trigonometric functions we get,
cos2x= 1 2 3 2 + 3 2 1 2   cos2x= 3 4 + 3 4   cos2x=  3 2   cos2x=cos 30 °   2x= 30 °   x= 15 °  
Thus the value will be 15 °  .
Therefore the correct option is 2.
 
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