March 31st, 2007, 09:13 PM  #1 
Newbie Joined: Jan 2007 Posts: 18 Thanks: 0  Exact values
I am looking for help on this one: If [theta] is an acute angle with sin[theta]=3/5, find the exact value of cos 2[theta]. I think it's 24/25 but I am really just guessing. 
April 1st, 2007, 02:01 AM  #2 
Site Founder Joined: Nov 2006 From: France Posts: 824 Thanks: 7 
Use cos^2(x)=1sin^2(x) and cos(2x)=2cos^2(x)1 to get cos(2x)=12sin^2(x).


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