Question

三道数学题

1996x19951995减1995x19961996
(1x2)/1+(2x3)/1+(3x4)/1......+(19x20)/1
(1x4)/1+(4x7)/1+(7x10)/1......+(91x94)/1

Answer 1

1996x19951995-1995x19961996
=1996×1995×10001-1995×1996×10001
=0

(1x2)/1+(2x3)/1+(3x4)/1......+(19x20)/1
=1-2/1+2/1-3/1+3/1-4/1+……+19/1-20/1
=1-20/1
=20/19

(1x4)/1+(4x7)/1+(7x10)/1......+(91x94)/1
=（1-4/1+4/1-7/1+7/1-10/1+……+91/1-94/1）÷3
=（1-94/1）÷3
=94/93÷3
=94/31

Answer 2

是在我的脑海里

Answer 3

1996x19951995减1995x19961996
=1996×1995×10001-1995×1996×10001
=0

(1x2)/1+(2x3)/1+(3x4)/1......+(19x20)/1
=1/1-1/2+1/2-1/3+1/3-1/4+……1/19-1/20
=1-1/20
=19/20

(1x4)/1+(4x7)/1+(7x10)/1......+(91x94)/1
=（1/1-1/4+1/4-1/7+……+1/91-1/94）×1/3
=（1-1/94）×1/3
=93/94×1/3
=31/94