Posted by **Rachel** on Monday, February 23, 2009 at 8:15pm.

sin^4 x = (3-4cos 2x + cos4x)/8

prove on one side please!

- trig -
**myschic**, Monday, February 23, 2009 at 8:21pm
just simplify both sides! easy as that!!!

- trig -
**Rachel**, Monday, February 23, 2009 at 8:33pm
how?

- trig -
**Reiny**, Monday, February 23, 2009 at 9:21pm
RS

= (3 - 4cos(2x) + cos^2(2x) - sin^2(2x))/8

= (3 - 4cos(2x) + cos^2(2x) - (1 - cos^2(2x)))/8

= (2cos^2(2x) - 4cos(2x) + 2)/8

= (2(cos^2(2x) - 2cos(2x) + 1))/8

= (2(cos(2x) - 1)^2)/8

= (2(1 - 2sin^2(x) - 1)^2)/8

= (2(-2sin^2(x))^2)/8

= (8sin^4(x))/8

= sin^4(x)

= LS

hope I made no typos this time

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