genepeer Posted October 22, 2010 Report Share Posted October 22, 2010 It's a Paper 1 question that means no calculator. Here it goes:sin(4x) = sin(x), 0 < x < pi. Reply Link to post Share on other sites More sharing options...
adletaY Posted October 23, 2010 Report Share Posted October 23, 2010 Interesting . . . you have to use De Moivre's theorem to figure this out, I'll give it a shot and post my answer here. Reply Link to post Share on other sites More sharing options...
sprintdominator Posted October 28, 2010 Report Share Posted October 28, 2010 LOL De moivre????!?!? sin4X - sinX =0=> sin 4x = sin x=> 4x = kπ + (-1)^k * xk = 0 => x = 0k = 1 => x = π/5k =2 => x = 2π/3k = 3 => x = 3π/5k = 4 => x = 4π/3k = 5 => x = π Reply Link to post Share on other sites More sharing options...
Mahuta ♥ Posted October 28, 2010 Report Share Posted October 28, 2010 I didn't try to work it out, but normally in these kind of questions they expect you to use all the rules and formula related to sine and cosine...etc..etc. Reply Link to post Share on other sites More sharing options...
sprintdominator Posted October 28, 2010 Report Share Posted October 28, 2010 or alternatively,sin4x=sinxsin4x-sinx=0using factor formula,sin4x-sinx= 2cos5/2xsin3/2x2cos2.5xsin1.5x=0cos2.5x=0or sin1.5x=0solve 2 Reply Link to post Share on other sites More sharing options...
genepeer Posted October 28, 2010 Author Report Share Posted October 28, 2010 (edited) using factor formula,sin4x-sinx= 2cos5/2xsin3/2xThat factor formula is nice!! Edited October 28, 2010 by Gene-Peer Reply Link to post Share on other sites More sharing options...
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