2/3 < 3/4,
4/5 < 5/6,...
2n/(2n+1) < (2n+1)/(2n+2)..
So:
(（2×4×6×……×2n）/（3×5×7×……×（2n+1））)^2
< (2/3)* (3/4)*(4/5)*(5/6)*...*((2n)/(2n+1))*((2n+1)/(2n+2))
= 2/(2n+2)=1/(n+1)---> 0