ronald172009 Posts: 1, Reputation: 1 New Member #1 Jun 29, 2012, 04:28 AM
prove trig identities solver
Prove cos^4 x - sin^4 x = cos 2x
 ebaines Posts: 12,132, Reputation: 1307 Expert #2 Jun 29, 2012, 06:50 AM
Note that the equation is the difference of two squares - so you can factor it. After that see if what you get looks like an identity for cos2x.

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