Tính bằng cách hợp lí nhất
a) A = \(\frac{\left(1+17\right)\left(1+\frac{17}{2}\right)\left(1+\frac{17}{3}\right)...\left(1+\frac{17}{19}\right)}{\left(1+19\right)\left(1+\frac{19}{2}\right)\left(1+\frac{19}{3}\right)..\left(1+\frac{19}{17}\right)}\)
b) B = \(\left(\frac{1}{2}-1\right)\left(\frac{1}{3}-1\right)...\left(\frac{1}{99}-1\right)\left(\frac{1}{100}-1\right)\)