(1-四分之一)(1-九分之一)(1-十六分之一).(1- 144分之1)(1-169分之1)
=(1+1/2)(1-1/2)(1+1/3)(1-1/3)(1+1/4)(1-1/4)……(1+1/12)(1-1/12)(1+1/13)(1-1/13)
=3/2x4/3x5/4x……x13/12x14/13x1/2x2/3x3/4x……x11/12x12/13
=14/2x1/13
=7/13
(1-四分之一)(1-九分之一)(1-十六分之一).(1- 144分之1)(1-169分之1)
=(1+1/2)(1-1/2)(1+1/3)(1-1/3)(1+1/4)(1-1/4)……(1+1/12)(1-1/12)(1+1/13)(1-1/13)
=3/2x4/3x5/4x……x13/12x14/13x1/2x2/3x3/4x……x11/12x12/13
=14/2x1/13
=7/13