October 14th, 2010, 07:01 PM  #1 
Member Joined: Sep 2010 Posts: 55 Thanks: 0  Sine
If sin(xpi)=A sin x, then the number A=___ I don't even know where to start. Please help. 
October 14th, 2010, 07:55 PM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs  Re: Sine
sin(x  ?) = A sin(x) Use the additive angle identity for sine: sin(a ± b) = sin(a)cos(b) ± cos(a)sin(b). sin(x)cos(?)  cos(x)sin(?) cos(?) = 1, sin(?) = 0, thus sin(x) = A sin(x) 0 = (sin(x))(A + 1) For sin(x) ? 0, A = 1 
October 15th, 2010, 06:43 PM  #3 
Global Moderator Joined: Dec 2006 Posts: 21,034 Thanks: 2271  Re: Sine
Learn the identities below. sin(A) ? sin(A), cos(A) ? cos(A), tan(A) ? tan(A) (if defined) sin(A) ? sin(?  A), cos(A) ? cos(?  A), tan(A) ? tan(?  A) (if defined) sin(A) ? sin(A + 2?), cos(A) ? cos(A + 2?), tan(A) ? tan(A + ?) (if defined) They imply that sin(x  ?) ? sin(?  x) ? sin(x) ? (1)sin(x). 

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