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 April 20th, 2014, 04:24 AM #1 Senior Member   Joined: Nov 2013 Posts: 434 Thanks: 8 complex z = cos(x) + isin(x) prove that 2/(1-z) = 1 + icot(x/2) Last edited by skipjack; April 20th, 2014 at 02:16 PM. Reason: to add parentheses
 April 20th, 2014, 02:11 PM #2 Global Moderator   Joined: Dec 2006 Posts: 20,919 Thanks: 2202 cot(x/2) = (1 + cos(x))/sin(x), so (1 - cos(x) - isin(x))(1 + i(1 + cos(x))/sin(x)) = 1 - cos(x) + (1 + cos(x)) - isin(x) + i(1 - cos²(x))/sin(x) = 2.
 April 20th, 2014, 02:25 PM #3 Global Moderator   Joined: Dec 2006 Posts: 20,919 Thanks: 2202 Trigonometry problems should not normally be posted in the algebra subforum or the geometry subforum.

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