1、（1-1/2的平方）*（1-1/3的平方）*.*（1-1/2004的平方）
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)*...*(1-1/2004)(1+1/2004)
=1/2*3/2*2/3*4/3*...*2003/2004*2005/2004
=1/2*(3/2*2/3)*(4/3*3/4)*...*(2004/2003*2003/2004)*2005/2004
=1/2*2005/2004
=2005/4008
2、1又1/4-9\20+11\30-13\42+15\56
=1+1/4-(4/20+5/20)+(5/30+6/30)-(6/42+7/42)+(7/56+8/56)
=1+1/4-1/5-1/4+1/5+1/6-1/6-1/7+1/7+1/8
=1+1/8
=1又1/8
3、（19/96+1919/9696+191919/969696）除以19191919/96969696
=(19/96+19*101/96*101+19*10101/96*10101)÷(19*1010101)/(96*1010101)
=(19/96+19/96+19/96)÷(19/96)
=19/96×3÷19/96
=3