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March 31st, 2007, 08:13 PM   #1
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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.
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April 1st, 2007, 01:01 AM   #2
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Use cos^2(x)=1-sin^2(x) and cos(2x)=2cos^2(x)-1 to get cos(2x)=1-2sin^2(x).
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