Look at the proof showing sin^4x=3-4cos2x+cos4x/8. which expression will complete the fourth step of the proof? sin^4x=(sin^2x)^2 sin^4x=(1-cos2x/2)^2 sin^4x=1-2cos2x+cos^22x/4 sin^4x=? a.) 1-2cos2x+(1+cos4x/2)/4 b.)1-2cos2x+1+cos4x/4 c.)1-2cos2x+(1+cos2x/2)/4 d.)1-2cos2x+1-cos2x/4