已知数列种,a1=1,an·an-1（n和n-1都为底数）=an-1+(-1)^n(n≥2）,求a3/a5.

Question

已知数列种,a1=1,an·an-1（n和n-1都为底数）=an-1+(-1)^n(n≥2）,
求a3/a5.

Answer 1

a2*a1=a1+1,a2=2
a3*a2=a2-1,a3=1/2
a4*a3=a3+1,a4=3
a5*a4=a4-1,a5=2/3
a3/a5=(1/2)/(2/3)=3/4