how do u prove this identity?? 2009 on

[1992]

cos4@ - 4cos2@ + 3 = 8sin^4@
with working out needed pleasee

 

[smuz_717]

(2cos^2 (2@) - 1) - 4( 1 - 2sin^2 @) + 3
2(1-2sin^2 @)^2 -1- 4 + 8sin^2 @ + 3
2( 1 - 4sin^2 @ + 4sin^4 @ ) - 2 + 8sin^2 @
2 - 8sin^2 @ + 8sin^4 @ - 2 + 8sin^2 @
8sin^4 @

 

[ammadb]

yep its simple .. open up cos4@ twice with the formula cos2@ = 2cos^2@ - 1 ..
do this for both cos.. sovle it ur ans will come =)