(1-1/2^2)(1-1/3^2)(1-1/4^2)……(1-1/10^2)
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4)...(1-1/10)(1+1/10)
=1/2*3/2*2/3*4/3*3/4*5/4*...*9/10*11/10
=1/2*11/10
=11/20
(1-1/2^2)(1-1/3^2)(1-1/4^2)……(1-1/10^2)
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4)...(1-1/10)(1+1/10)
=1/2*3/2*2/3*4/3*3/4*5/4*...*9/10*11/10
=1/2*11/10
=11/20