Question

calcule cos 2x, sabendo que sen x = 2/7

Answer 1

 

$<var>como: 1) (Sen x)^{2}+(Cos x)^{2} = 1 </var></p> <p><var>2) Cos 2x= (Cos x)^{2} - ( Sen x)^{2} </var></p> <p> </p> <p><var>Somando 1) e 2) ,</var><var>temos: </var></p> <p> </p> <p><var>Cos 2x=1-2*(sen x)^{2}</var></p> <p> </p> <p><var>Assim: </var></p> <p><var> Cos 2x = 1-2*((2/7)^{2}) </var></p> <p><var>Cos 2x=1-8/49 </var></p> <p><var>Cos 2x=(41/49) =0,8367346</var>$