(1-2方分之一)(1-3方分之一)(1-4方分之一)(1-5方分之一)
=(1+1/2)(1-1/2)(1+1/3)(1-1/3)(1+1/4)(1-1/4)(1+1/5)(1-1/5)
=3/2×4/3×5/4×6/5×1/2×2/3×3/4×4/5
=6/2×1/5
=3/5
(1-2方分之一)(1-3方分之一)(1-4方分之一)(1-5方分之一)
=(1+1/2)(1-1/2)(1+1/3)(1-1/3)(1+1/4)(1-1/4)(1+1/5)(1-1/5)
=3/2×4/3×5/4×6/5×1/2×2/3×3/4×4/5
=6/2×1/5
=3/5