1.

The value of cos^(2)10^(@)-cos10^(@)cos 50^(@)is k/2 . The value of k is ________.

Answer»


SOLUTION :`COS^(2)10^(@)-cos10^(@)cos50^(@)+cos^(2)50^(@)`
`=1/2 [ 2 cos^(2) 10^(@)-2cos10^(@)cos 50^(@)+2cos^(2)50^(@)]=1/2[1+cos20^(@)-cos40^(@)-cos60^(@)+1+cos 100^(@)]`
`=1/2[3/2 + (cos 20^(@)-cos40^(@))+cos(90^(@)+10^(@))]=1/2[3/2 +2*sin30^(@)SIN 10^(@)-sin 10^(@)]=3/4`


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