a1=1/4 f(1)=1-a1=3/4
a2=1/9 f(2)=3/4*8/9=2/6=1/3
a3=1/16 f(3)=1/3 * 15/16=5/16.
推导f(n)的值:
a(n)=1/(n+1)^2
设b(n)=1-a(n)=1-1/(n+1)^2=[(n+1)^2-1]/(n+1)^2=n(n+2)/(n+1)^2
f(n)=b(1)*b(2)*...*b(n)=1*3/2^2* 2*4/3^2*...* n(n+2)/(n+1)^2=(n+2)/[2(n+1)]
a1=1/4 f(1)=1-a1=3/4
a2=1/9 f(2)=3/4*8/9=2/6=1/3
a3=1/16 f(3)=1/3 * 15/16=5/16.
推导f(n)的值:
a(n)=1/(n+1)^2
设b(n)=1-a(n)=1-1/(n+1)^2=[(n+1)^2-1]/(n+1)^2=n(n+2)/(n+1)^2
f(n)=b(1)*b(2)*...*b(n)=1*3/2^2* 2*4/3^2*...* n(n+2)/(n+1)^2=(n+2)/[2(n+1)]