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 October 14th, 2010, 07:01 PM #1 Member   Joined: Sep 2010 Posts: 55 Thanks: 0 Sine If sin(x-pi)=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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