Sin⁴b+cos⁴b=(3+cos4b)/4;

(sin⁴b+2sin²b*cos²b+cos⁴b)-2sin²b*cos²b=

(sin²b+cos²b)²-0,5(2sinb*cosb)(2sinb*cosb)=1-0,5sin²2b=

1-0,5(1-cos4b)/2=4/4-(1-cos4b)/4=(4-1+cos4b)/4=(3+cos4b)/4;

(3+cos4b)/4=(3+cos4b)/4;