5+(-5)+6+(-6)+7+(-7)+100=?
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\(\dfrac{7}{10}=0,7;\dfrac{7}{100}=0,07;6\dfrac{38}{100}=6,38;\dfrac{2014}{1000}=2,014;\dfrac{3}{2}=1,5;\dfrac{2}{5}=0,4;\dfrac{5}{8}=0,625;1\dfrac{1}{4}=1,25;6\dfrac{38}{100}=6,38\)
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2.(1+2+3+4+.....+100).(89.2)
2.5050.89.2
2(5050.89)
=898900
(1+1+2+2+3+3+4+4+5+5+6+6+...+100+100)* (89 *2 )
=(1+100)+(1+100)+(2+99)+...+(54+57)+(55+56)+(55+56)*187
=101+101+101+...+101+101+101*187
=101*100*187
=10100*187=1888700
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1+1+2+2+2+3+3+3+3+4+4+4+5+5+5+6+6+6+7+7+7+...+99+99+99+100
= (1x2)+(2x3)+(3x3)+(4x3)+(5x3)+(6x3)+(7x3)+...+(99x3)+100
=2x6x9x12x15x18x21x...x297+100
=(297-2) : 3 + 1 +100
ok , phần còn lại tự tính nha bạn
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![](https://rs.olm.vn/images/avt/0.png?1311)
theo đề bài ta có :
2(1+2+3+4+5+6+7+8+9+10+11+.....+100)
=2x5050
=10100
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{5}{6\cdot7}+\frac{5}{7\cdot8}+\frac{5}{8\cdot9}+...+\frac{5}{100\cdot101}\)
\(=5\left(\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}+...+\frac{1}{100\cdot101}\right)\)
\(=5\left(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+...+\frac{1}{100}-\frac{1}{101}\right)\)
\(=5\left(\frac{1}{6}-\frac{1}{101}\right)\)
\(=5\left(\frac{95}{606}\right)\)
\(=\frac{475}{606}\)
Tính
\(\frac{5}{6\times7}+\frac{5}{7\times8}+\frac{5}{8\times10}+...+\frac{5}{100\times101}\)
\(=5\times\left(\frac{1}{6\times7}+\frac{1}{7\times8}+\frac{1}{8\times9}+...+\frac{1}{100\times101}\right)\)
\(=5\times\left(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+...+\frac{1}{100}-\frac{1}{101}\right)\)
\(=5\times\left(\frac{1}{6}-\frac{1}{101}\right)\)
\(=5\times\frac{95}{606}=\frac{475}{606}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Mình làm mẫu 1 bài rùi bạn tự giải những bài còn lại nha
1, 7A = 7+7^2+7^3+....+7^2008
6A = 7A - A = (7+7^2+7^3+....+7^2008)-(1+7+7^2+....+7^2007) = 7^2008-1
=> A = (7^2008-1)/6
Tk mk nha
\(A=1+7+7^2+7^3+...+7^{2007}\)
\(\Rightarrow7A=7+7^2+7^3+7^4+...+7^{2008}\)
\(\Rightarrow7A-A=\left(7+7^2+7^3+...+7^{2008}\right)-\left(1+7+7^2+...+7^{2007}\right)\)
\(\Rightarrow6A=7^{2008}-1\)
\(\Rightarrow A=\frac{7^{2008}-1}{6}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
= 0 + 0 + 0 + 100
= 0 + 100
= 100
= 0 + 0 + 0 + 100
= 0 + 100
=100