1-2+3-4+5-6+...+2009-2010
tính các dãy số sau:
-1-2+3+4-5-6+7+8-.....-2009-2010+2011
-1-2+3-4-5+6+....-2009+2010-2011
tinh tong
a)s=1+(-2)+3+(-4)+.......+2009+(-2010)
b)s=1+(-2)+(-3)+4+5+6(-6)+(-7)+......+2008+2009+(-2010)
Tính tổng:
a,S1=1+(-2)+3+(-4)+..........+2009+(-2010)
b,S2=1+(-2)+(-3)+4+5+(-6)+(-7)+............+2008+2009+(-2010)
a,S1=1+(-2)+3+(-4)+..........+2009+(-2010)
S1=-1.(2010:2)
S1=-1005
b,S2=1+(-2)+(-3)+4+5+(-6)+(-7)+............+2008+2009+(-2010)
S2=-1.(2010:2)
S2=-1.1005
S2=-1005
1/2*2/3*3/4*4/5*5/6*.....*2009/2010
\(\frac{1}{2}\cdot\frac{2}{3}\cdot\frac{3}{4}\cdot\frac{4}{5}\cdot....\cdot\frac{2009}{2010}\)
\(=\frac{\left(2\cdot3\cdot4\cdot5....\cdot2009\right)}{\left(2\cdot3\cdot4\cdot5\cdot....\cdot2009\right)\cdot2010}=\frac{1}{2010}\)
1/2x2/3x3/4x4/5x5/6x......x2009/2010
=(2x3x4x5x.....x2009)/(2x3x4x5x......x2009).2010=1/2010
Cho A = 1/2001+2/2009+3/2008+........2009/+ 2010/1, B = 1+1/2+1/3+1/4+1/5+1/6+.......1/2010+1/2011. Tính A/B
Tính tổng sau
A=1-2+3-4+5-....-2008+2009
B=1+2-3-4+5+6-7-...-2007-2008+2009+2010
Bài làm:
\(A=1-2+3-4+5-...-2008+2009\)
\(A=\left(1-2\right)+\left(3-4\right)+\left(5-6\right)+...+\left(2007-2008\right)+2009\)
\(A=-1-1-1-...-1+2009\)(1004 số -1)
\(A=-1004+2009=1005\)
\(B=1+2-3-4+5+6-7-...-2007-2008+2009+2010\)
\(B=1+\left(2-3-4+5\right)+\left(6-7-8+9\right)+...+\left(2006-2007-2008+2009\right)+2010\)
\(B=1+0+0+...+0+2010\)
\(B=2011\)
Học tốt!!!!
Tính:\(^{1^2}\)
a) 1^2-2^2+3^2-4^2+5^2-6^2+....+2009^2-2010^2
b) 3^2010-(3^2009+3^2008+3^2007+...+3+3^0)
1 – 2 + 3 – 4 + 5 – 6 + … + 2009 – 2010 + 2011
1 – 2 + 3 – 4 + 5 – 6 + … + 2009 – 2010 + 2011
= ( 1-2)+(3-4)+(5-6)+......+(2009-2010)+2011
=(-1)+(-1)+(-1)+.....+(-1)+2011
=(-1)x1005+2011
=(-1005)+2011
=1006
Lời giải:
1−2+3−4+5−6+...+2009−2010+2011
Ta có:
(1−2)+(3−4)+(5−6)+...+(2009−2010)+2011
Có:2010số=>1005cặp số
=>1005.(−1)+2011=1006
Học tốt
1-2+3-4+5-6+...+2009-2010+2011
= ( 1 - 2 ) + (3-4) + ( 5-6) +...+ (2009- 2010)+2011
= (-1) + (-1) + (-1) + ... + ( - 1) + 2011
=(-1) . 1005 + 2011
= ( - 1005) + 2011
= 1006
1-2+3-4+5-6+..+2009-2010+2011
1 - 2 + 3 - 4 + 5 - 6 + ... + 2009 - 2010 + 2011
= (1 - 2) + (3 - 4) + (5 - 6) + ... + (2009 - 2010) + 2011
= (-1) + (-1) + (-1) + ... + (-1) + 2011
có 1005 số -1
= (-1).1005 + 2011
= -1005 + 2011
= 1006
1-2+3-4+5-6+......+2009-2010+2011
=(1-2)+(3-4)+(5-6)+....+(2009-2010)+2011
Từ 1 đến 2010 có 2010 số hạng
=(-1)+(-1)+(-1)+....+(-1)+2011
có 1005 số (-1)
=(-1)*1005+2011
=1006
1 - 2 + 3 - 4 + 5 - 6 + ...... + 2009 - 2010 + 2011
= (1 - 2) + (3 - 4) + (5 - 6) + ...... + (2009 - 2010) + 2011
= (-1) + (-1) + (-1) + ...... + (-1) + 2011
= (-1).1005 + 2011
= -1005 + 2011
= 1006