29²-28²=(29-28)(29+28)=1*57=57
B=7+5=12. b^2=144,144/7=20 остаток 4,b^4=20736,20736/7=2962 остаток 2
(1/5-1/4):(-1,6-3,3+5)=(0,2-0,25):0,1=-0,5
D=3.......................................................................................................................................................................................................