Bài 1:

a) \(B=1-\frac{2}{3.5}-\frac{2}{5.7}-\frac{2}{7.9}-...-\frac{2}{61.63}-\frac{2}{63.65}\)

\(B=1-\left(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{61.63}+\frac{2}{63.65}\right)\)

\(B=1-\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{61}-\frac{1}{63}+\frac{1}{63}-\frac{1}{65}\right)\)

\(B=1-\left(\frac{1}{3}-\frac{1}{65}\right)\)

\(B=1-\frac{62}{195}\)

\(B=\frac{133}{195}\)

b) \(C=1-\frac{1}{5.10}-\frac{1}{10.15}-\frac{1}{15.20}-...-\frac{1}{95.100}\)

\(C=1-\left(\frac{1}{5.10}+\frac{1}{10.15}+\frac{1}{15.20}+...+\frac{1}{95.100}\right)\)

\(C=1-\frac{1}{5}.\left(\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{95}-\frac{1}{100}\right)\)

\(C=1-\frac{1}{5}.\left(\frac{1}{5}-\frac{1}{100}\right)\)

\(C=1-\frac{1}{5}.\frac{19}{100}\)

\(C=1-\frac{19}{500}\)

\(C=\frac{481}{500}\)

bài 2 thì bn lm như bn Phùng Minh Quân nha!

Câu 1 : mình ko hiểu đề bài cho lắm ~.~ 

Câu 2 : 

Ta có : 

\(\left|\frac{1}{2}-x\right|\ge0\)

\(\Rightarrow\)\(A=10+\left|\frac{1}{2}-x\right|\ge10\)

Dấu "=" xảy ra \(\Leftrightarrow\)\(\left|\frac{1}{2}-x\right|=0\)

\(\Leftrightarrow\)\(\frac{1}{2}-x=0\)

\(\Leftrightarrow\)\(x=\frac{1}{2}\)

Vậy GTNN của \(A\) là \(10\) khi \(x=\frac{1}{2}\)

Chúc bạn học tốt ~ 

=(5/5-5/10+5/10-5/15+.........+5/2015-5/2020)

=(1/5-1/10+1/10-1/20+.......+1/2015-1/2020)

=1/5-1/2020

=403/2020

ai tích mk mk vs

\(\frac{5}{5.10}+\frac{5}{10.15}+.............+\frac{5}{2015.2020}\)

\(=\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+..............+\frac{1}{2015}-\frac{1}{2020}\)

\(=\frac{1}{5}-\frac{1}{2020}\)

\(=\frac{403}{2020}\)

5/5.10+5/10.15+5/15.20+...+5/2015.2020

=5(1/5.10+1/10.15+1/15.20+...+1/2015.2020) khoang cach tu 5-10;10-15;...;2015-2020 la 5 suy ra

=5/5(1/5-1/10+1/10-1/15+1/15-1/20+...+1/2015-1/2020)    ;   (-1/5+1/5;-1/10+1/10;-1/15+1/15;-1/20+1/20;... bang 0)

=1(1/5-1/2020)=2015/10100=403/2020

\(\frac{2}{5.10}+\frac{2}{10.15}+\frac{2}{15.20}+...+\frac{2}{2015.2020}\)

\(=2.\left(\frac{1}{5.10}+\frac{1}{10.15}+\frac{1}{15.20}+...+\frac{1}{2015.2020}\right)\)

\(=2.\left(\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{2015}-\frac{1}{2020}\right)\)

\(=2.\left(\frac{1}{5}-\frac{1}{2020}\right)\)

\(=2.\frac{403}{2020}=\frac{403}{1010}\)

\(\frac{2}{5.10}+\frac{2}{10.15}+\frac{2}{15.20}+...+\frac{2}{2015.2020}\)

=\(\frac{2}{5}\left(\frac{5}{5.10}+\frac{5}{10.15}+\frac{5}{15.20}+...+\frac{5}{2015.2020}\right)\)

=\(\frac{2}{5}\left(\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{2015}-\frac{1}{2016}\right)\)

=\(\frac{2}{5}.\left(\frac{1}{5}-\frac{1}{2020}\right)\)

=\(\frac{2}{5}.\frac{403}{2020}\)

=\(\frac{403}{5005}\)

a: \(A=5\cdot2\cdot\left(-3\right)-10+3\cdot\left(-3\right)=-30-10-9=-49\)

 b: \(B=8\cdot1\cdot\left(-1\right)^2-1\cdot\left(-1\right)-2\cdot1-10\)

=8+1-2-10

=-3

a: 

 b: 

=8+1-2-10

=-3

5/3

= 1/3 : 1/5 = 1/3 x 5 = 5/3

5\3

10.213

11. 2 giờ 55 phút

12. 4 ngày 21 giờ

13.

a: 6,008

b: 4500

c: 5,628

d: 4,009

=(45.5)^10/75^10

=(225/75)^10

=3^10

=59049

\(\frac{45^{10}\cdot5^{10}}{75^{10}}=\frac{3^{10}\cdot15^{10}\cdot5^{10}}{75^{10}}=\frac{3^{10}\cdot3^{10}\cdot5^{10}\cdot5^{10}}{3^{10}\cdot25^{10}}=\frac{3^{10}\cdot3^{10}\cdot5^{10}\cdot5^{10}}{3^{10}\cdot5^{10}\cdot5^{10}}=\frac{3^{20}\cdot5^{20}}{3^{10}\cdot5^{20}}=3^{10}\)

=(45.5)^10/75^10

=225^10/75^10

=(225/75)^10

=3^10

=59049