(a的2n-1次幂/b的3n-1次幂)*(b的3n-2次幂/a的2n次幂)=[a^(2n-1)/b^(3n-1)]*[(b^(3n-2)/a^(2n)]=[a^(2n-1)/a^(2n)]*[(b^(3n-2)/b^(3n-1)]=a^(2n-1-2n)*b^(3n-2-3n+1)=a^(-1)*b^(-1)=1/(ab)