(b-1)²(1/(b²-2b+1) + 1/(b²-1)) + 2/(b+1) = (b-1)²(1/(b-1)² + 1/(b-1)(b+1)) + 2/(b+1) = (b-1)²/(b-1)² + (b-1)²/(b-1)(b+1) + 2/(b+1) = 1 + (b-1)/(b+1) + 2/(b+1) = 1 + (b-1+2)/(b+1) = 1 + (b+1)/(b+1) = 1+1 = 2
равно 2 всегда, независимо от b
