2. 5^4*(0,2)^(-3)/125^2 = 5^4*5^3/(5^3)^2 = 5^7/5^6 = 5
3. Умножаем все на х
x^2 + 81 = 18x
x^2 - 18x + 81 = 0
(x - 9)^2 = 0
x1 = x2 = 9
4. Сделаем по действиям.
1) (b+1)/(b-1) - b/(b+1) = ((b+1)^2 - b(b-1))/((b-1)(b+1)) = (b^2+2b+1-b^2-b)/((b+1)(b-1)) =
= (b+1)/((b+1)(b-1) = 1/(b-1)
2) 1/(b-1) : (3b+1)/(2b-2) = 1/(b-1)*2(b-1)/(3b+1) = 2/(3b+1)