Объясните решение.

3-4cos2B+cos4B / 3+4cos2B+cos4B = tg^4B

Tg%4b=sin^4b/cos^4b = (1-cos2b) ² / (1+cos2b) ²=

= (1-2cos2b+cos²2b) / (1+2cos2b+cos²2b) =

=[1-cos2b + (1+cos4b) / 2]/[1+cos2b + (1+cos4b) / 2]=

= (2-2cos2b+1+cos4b) / (2+2cos2b+1+cos4b) =

= (3-cos2b+cos4b) / (3+cos2b+cos4b)

чтд