Докажите тождество (5+b/5-b - 20b/25-b^2) : 5-b/4 = 4/5+b

1) (5+в)/(5-в)-20в/(25-в^2)=((5+в)^2-20в)/(25-в^2)=(25+10в+в^2-20в)/(25-в^2)=(в^2-10в+25)/(25-в^2)=(в-5)^2/(25-в^2)=(5-в)^2/(5-в)(5+в)=(5-в)/(5+в).
2) (5-в)/(5+в)*4/(5-в)=4/(5+в).
3)4/(5+в)=4/(5+в) - тождество доказано.