wheyard
春芽
共回答了20个问题采纳率:95% 举报
1
分成两个式子,+号的和-号的分开来
(1+1/2)*(1+1/3)*(1+1/4)*……*(1+1/100)
=3/2*4/3*5/4*6/5*……*100/99+101/100=101/2
(前一个分子和后一个分母相消了)
减号的式*子同理
=1/2*2/3*3/4*……*98/99*99/100=1/100
(前一个分母和后一个分子相消了)
两个相乘等于101/200
2
(1999+2000x1998)/(1999x2000-1 )
=(1999+2000x1998)/(1998x2000+2000-1)
=(1999+2000x1998)/(1998x2000+1999)
=1
3
(2002x1999-1957)/(42+1999x2001)
=(2001x1999+1999-1957)/(42+1999x2001)
=(2001x1999+42)/(42+1999x2001)
=1
4
1/2x4+1/4x6+1/8x10+1/10x12
=(1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12)÷2
=(1/2-1/12)÷2
=5/12÷2
=5/24
1年前
2