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 Pre-Calculus Pre-Calculus Math Forum

 February 28th, 2016, 01:38 PM #1 Newbie   Joined: Feb 2016 From: washington Posts: 4 Thanks: 0 Prove Question I can't seem to get the answer but I think I'm close. The question is sin^4(x) - cos^4(x) = 1 - 2cos^2(x) I got sin^2(x)-cos^2(x)/sin^2(x)+cos^2(x), trying to prove LHS. Thanks ! February 28th, 2016, 01:50 PM #2 Math Team   Joined: Jul 2011 From: Texas Posts: 3,016 Thanks: 1600 $\sin^4{x}-\cos^4{x}=$ $(\sin^2{x}-\cos^2{x})(\sin^2{x}+\cos^2{x})=$ $(\sin^2{x}-\cos^2{x}) \color{red}{(1)}=$ $(1-\cos^2{x})-\cos^2{x}=$ $1-2\cos^2{x}$ Thanks from v8archie and Country Boy Last edited by skeeter; February 28th, 2016 at 02:08 PM. Tags prove, question Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post jiasyuen Calculus 5 December 23rd, 2013 04:58 AM 450081592 Applied Math 1 September 15th, 2010 03:35 AM 450081592 Linear Algebra 1 February 25th, 2010 02:16 AM igalep132 Calculus 8 February 7th, 2008 04:36 AM jiasyuen Algebra 0 December 31st, 1969 04:00 PM

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