\(A=1\times3+2\times4+3\times5+4\times6+...+197\times199+198\times200\)

\(B=1\times3+3\times5+...+197\times199\)

\(6\times B=1\times3\times\left(5+1\right)+3\times5\times\left(7-1\right)+5\times7\times\left(9-3\right)+...+197\times199\times\left(201-195\right)\)

\(=1\times3+1\times3\times5+3\times5\times7-1\times3\times5+...+197\times199\times201-195\times197\times199\)

\(=1\times3+197\times199\times201\)

\(B=1313301\)

\(C=2\times4+4\times6+...+198\times200\)

\(6\times C=2\times4\times6+4\times6\times\left(8-2\right)+...+198\times200\times\left(202-196\right)\)

\(=2\times4\times6+4\times6\times8-2\times4\times6+...+198\times200\times202-196\times198\times200\)

\(=198\times200\times202\)

\(C=1333200\)

\(A=B+C=1313301+1333200=2646501\)

Xét: 3/(1.2)=(1+2)/(1.2)=1/2+1

5/(2.3)=(2+3)/(2.3)=1/3+/1/2

7/(3.4)=(3+4)/(3.4)=1/4+1/3

...

2021/(1010.1011)=(1010+1011)/(1010.1011)=1/1010+1/1011

Do đó: Q=1+1/2-1/2-1/3+1/3+1/4-...-1/1010-1/1011

=1-1/1011

=1010/1011

sai thì sorry nha, nhưng cách làm là đúng rồi

Lê Gia Long e lớp 4 thì ko đc lm!

\(Q=\frac{3}{1\cdot2}-\frac{5}{2\cdot3}+\frac{7}{3\cdot4}...-\frac{2021}{1010\cdot1011}\)

\(=\left(\frac{1}{1}+\frac{1}{2}\right)-\left(\frac{1}{2}+\frac{1}{3}\right)+\left(\frac{1}{3}+\frac{1}{4}\right)...-\left(\frac{1}{1010}-\frac{1}{1011}\right)\)

\(=1-\frac{1}{1011}\)

\(=\frac{1010}{1011}\)

\(2^2+\left(x+3\right)=3^2\)

\(4+\left(x+3\right)=9\)

\(x+3=9-4\)

\(x+3=5\)

\(x=5-3\)

\(x=2\)

Vậy \(x=2\)

Bài 3: 

a) Sau hai ngày thì người thợ sơn còn phải sơn nốt số phần ngôi nhà là: 

\(1-\frac{1}{5}-\frac{1}{4}=\frac{11}{20}\)(ngôi nhà) 

b) Chiều rộng là: 

\(60\times\frac{2}{3}=40\left(m\right)\)

Diện tích mảnh vườn là: 

\(60\times40=2400\left(m^2\right)\)

gfvfvfvfvfvfvfv555

gfvfvfvfvfvfvfv555

b) \(\frac{11}{12}.\frac{31}{32}+\frac{63}{32}.\frac{-11}{12}\)

\(=\frac{11}{12}.\frac{31}{32}+\frac{-63}{32}.\frac{11}{12}\)

\(=\frac{11}{12}.\left(\frac{31}{32}+\frac{-63}{32}\right)\)

\(=\frac{11}{12}.\frac{-32}{32}\)

\(=\frac{11}{12}.\left(-1\right)\)

\(=\frac{-11}{12}\)

11/12.31/32+-63/32.11/12
= 11/12 ( 31/32+ -63/32 
= 11/12 . 1
=11/12 
Vì là nhân nên bn có thể đổi dấu bt đc nha

No copy*
Vui lòng k cho mik ặ =33

\(\frac{2}{5}-3.\left(x+\frac{3}{4}\right)=150\%\text{ }\)

\(\frac{2}{5}-3.\left(x+\frac{3}{4}\right)=\frac{3}{2}\)

\(3.\left(x+\frac{3}{4}\right)=\frac{2}{5}-\frac{3}{2}\)

\(3.\left(x+\frac{3}{4}\right)=\frac{-11}{10}\)

\(x+\frac{3}{4}=\frac{-11}{10}\div3\)

\(x+\frac{3}{4}=\frac{-11}{30}\)

\(x=\frac{-11}{30}-\frac{3}{4}\)

\(x=\frac{-67}{60}\)

Vậy \(x=\frac{-67}{60}\)

`Answer:`

\(\frac{x-10}{30}+\frac{x-14}{43}+\frac{x-5}{95}+\frac{x-148}{8}=0\)

\(\Leftrightarrow\frac{x-10}{30}+\frac{x-14}{43}+\frac{x-5}{95}+\frac{x-100}{8}-6=0\)

\(\Leftrightarrow\left(\frac{x-10}{30}-3\right)+\left(\frac{x-14}{43}-2\right)+\left(\frac{x-5}{95}-1\right)+\frac{x-100}{8}=0\)

\(\Leftrightarrow\frac{x-100}{30}+\frac{x-100}{43}+\frac{x-100}{95}+\frac{x-100}{8}=0\)

\(\Leftrightarrow\left(x-100\right)\left(\frac{1}{30}+\frac{1}{43}+\frac{1}{95}+\frac{1}{8}\right)=0\)

Mà \(\frac{1}{30}+\frac{1}{43}+\frac{1}{95}+\frac{1}{8}\ne0\)

\(\Rightarrow x-100=0\Leftrightarrow x=100\)