b)
A=1.2+2.3+3.4+...+2010.2011
3A=1.2.3+2.3.3+3.4.3+...+2010.2011.3
3A=1.2.3+2.3.(4-1)+3.4.(5-2)+...+2010.2011.(2012-2009)
=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...-2009.2010.2011+2010.2011.2012
=2010.2011.2012
=>A=2010.2011.2012 / 3
=2710908440
1.2+2.3+3.4+.....+2010.2011
1/24+1/60+1/120+...+1/6840
A=1.2+2.3+3.4+......+2010.2011
P/S dấu chấm . là dấu nhân
\(rút gọn biểu thức A = 1.2 + 2.3 +3.4+ ...+ 2010.2011\)
tinh gia tri bieu thuc :B=1.2+2.3+3.4+...+2010.2011
1/1.2+1/2.3+1/3.4+...+1/59.60= /60
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
Bài 6 : Tính tổng.
a,1/8 + 1/24 + 1/48 +......+ 1/10200
b,3/1.2 + 3/2.3 + 3/3.4 +......+ 3/2015.2016
Tính nhanh A = 1/1.2 + 1/2.3 + 1/3.4 + 1/3.4 + ... + 1/49.50
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
