Tính nhanh:
1)1.2+2.3+3.4+4.5+...+99.100
2) 1:20+1:44+1:77+1:119+1:170
Tính nhanh
C=1.2+2.3+3.4+...+2014.2015
K=1.2+2.3+3.4+..+(n-1).n
Bài 1:Tính:
a,3 14/19 + 13/17 + 35/43 + 6 5/19 + 8/13
b,130 25/28 + 120 17/35
c,17 2/31 - (15/17 + 6 2/31)
d,(31 6/13 + 5 9/41) - 31 6/13
e,(17 24/31 - 3 7/8) - (2 38/31 - 4)
g,1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6
h,1/1.2 + 1/2.3 + 1/3.4 + .........+ 1/49.100
i,1/1.3 + 1/3.5 + 1/5.7 +........+ 1/97.99
Tính nhanh A = 1/1.2 + 1/2.3 + 1/3.4 + 1/3.4 + ... + 1/49.50
Tính :
1/1.2 + 1/2.3 + 1/3.4 + . . . + 1/99.100
cho A = 1/1.2+1/2.3+1/3.4+...+1/49.50 ; cho B = 1.2+1.3+3.4+....+49.50
tính 50mủ 2A - B/17
tính A = 1/1.2 + 1/2.3 + 1/3.4 + ... + 1/2013.2014
Tính: A= 1 - 1/1.2 - 1/2.3 - 1/3.4 - ...- 1/97.98
Tính -1/1.2+-1/2.3+-1/3.4+...+-1/2015.2016+1/2016=?