My Math Forum Cosine approximation

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 July 30th, 2018, 08:21 AM #1 Newbie   Joined: Jul 2018 From: Asia Posts: 9 Thanks: 1 Cosine approximation how to arrive at (9.11) from (9.10) ? I am stucked during the steps
 July 30th, 2018, 12:42 PM #2 Global Moderator   Joined: May 2007 Posts: 6,822 Thanks: 723 $\cos(w_{in}-w_{in})t-\cos(w_{in}+w_{in})t =\cos^2w_{in}t+\sin^2w_{in}t-\cos^2w_{in}t+\sin^2w_{in}t=2\sin^2w_{in}t$ This may help. Thanks from topsquark and romsek Last edited by skipjack; August 1st, 2018 at 02:08 PM.
 August 1st, 2018, 05:01 AM #3 Newbie   Joined: Jul 2018 From: Asia Posts: 9 Thanks: 1 but the integral of sin() gives -cos() ? Do you have any further suggestions ?
 August 1st, 2018, 01:27 PM #4 Global Moderator   Joined: May 2007 Posts: 6,822 Thanks: 723 The term with the integral inside the bracket must be small for the approximation to make sense. Can you estimate it?
 August 1st, 2018, 02:21 PM #5 Global Moderator   Joined: Dec 2006 Posts: 20,969 Thanks: 2219 Is it really an indefinite integral? If so, how come no constant of integration is given? Thanks from topsquark
 August 1st, 2018, 06:34 PM #6 Newbie   Joined: Jul 2018 From: Asia Posts: 9 Thanks: 1 Vm is assumed to be of small magnitude. <-- How does this help in the approximation towards expression (9.11) ? Thanks from topsquark Last edited by promach; August 1st, 2018 at 06:38 PM.

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