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If x=sin70^(0). sin50^(0)and y = cos60^(@). cos80^(0),then what is xy equal to ? |
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Answer» `1//16` `rArrxy=cos60^(@).sin70^(@).sin50^(@).cos80^(@)` `xy=(1)/(2).sin(90-20)*sin(90-40)*cos80` `rArrxy=(1)/(2)*cos20*cos40*cos80` `(becausesin(90-x)=cosx)` `rArrxy=(1)/(2)*cos20^(@).cos(60-20)^(@).cos(60+20)^(@)` `rArrxy=(1)/(2)[(1)/(4)"cos"3(20^(@))]=(1)/(2)XX(1)/(4)xxcos60^(@)=(1)/(16)`. `[becausecostheta*cos(60-theta)*cos(60+theta)=(1)/(4)cos3theta]` |
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