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October 21, 2014

October 21, 2014

Posted by **Anonymous** on Sunday, April 15, 2012 at 12:01am.

im confused on this one cause of the 4th power of the sine. does this mean that we put it in the calculator 4 times? and what exactly does it mean by prove the identity- does it mean like make sure both sides equal each other?

- math -
**Bosnian**, Sunday, April 15, 2012 at 3:05amcos ^ 4( x ) - sin ^ 4 ( x ) =

[ cos ^ 2 ( x ) ] ^ 2 - [ sin ^ 2 ( x ) ] ^ 2 =

______________________________________

Remark:

a ^ 2 - b ^ 2 = ( a + b ) * ( a - b )

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= [ cos ^ 2 ( x ) + sin ^ 2 ( x ) ] *

[ cos ^ 2 ( x ) - sin ^ 2 ( x ) ] =

______________________________________

Remark:

cos ^ 2 ( x ) + sin ^ 2 ( x ) = 1

______________________________________

= 1 * [ cos ^ 2 ( x ) - sin ^ 2 ( x ) ] =

cos ^ 2 ( x ) - sin ^ 2 ( x ) =

______________________________________

Remark:

cos ^ 2 ( x ) = 1 - sin ^ 2 ( x )

______________________________________

= 1 - sin ^ 2 ( x ) - sin ^ 2 ( x ) =

1 - 2 sin ^ 2 ( x )

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