(1-1/2²)(1-1/3²)(1-1/4²)…(1-1/9²)(1-1/10²)
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4)(1-1/5)(1+1/5)(1-1/6)(1+1/6)(1-1/7)(1+1/7)(1-1/8)(1+1/8)(1-1/9)(1+1/9)(1-1/10)(1+11/10)
=1/2*3/2*2/3*4/3*3/4*.10/9*9/10*11/10
=1/2*11/10
=11/20
(1-1/2²)(1-1/3²)(1-1/4²)…(1-1/9²)(1-1/10²)
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4)(1-1/5)(1+1/5)(1-1/6)(1+1/6)(1-1/7)(1+1/7)(1-1/8)(1+1/8)(1-1/9)(1+1/9)(1-1/10)(1+11/10)
=1/2*3/2*2/3*4/3*3/4*.10/9*9/10*11/10
=1/2*11/10
=11/20