A)
(b-a)/a²b + (3a+b)/ab² - (3a²-4b²)/a²b² =
= [b(b-a) + a(3a+b) - 3a² - 4b²] / a²b² =
= (b²-ab+3a²+ab-3a²-4b²) / a²b² =
=-3b²/a²b² = -3/a²
б)
x/(2(x-1)) - 3/(2x+2) +(x-2)/(x²-1) =
= [x(x+1) - 3(x-1) + 2(x-2)] / 2(x-1)(x+1) =
= (x²+x-3x+3+2x-4) / 2(x-1)(x+1) =
= (x²-1) / 2(x-1)(x+1) =
=(x-1)(x+1) / 2(x-1)(x+1) =1/2