Posted by Rachel on .
sin^4 x = (34cos 2x + cos4x)/8
prove on one side please!

trig 
myschic,
just simplify both sides! easy as that!!!

trig 
Rachel,
how?

trig 
Reiny,
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