23 + 2 = 25

vì 25 - 23 = 2

23+2=25 nha

HT

\(\frac{1}{2}A=\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+......+\frac{1}{2^{11}}\)

\(\frac{1}{2}A-A=\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+......+\frac{1}{2^{11}}-\left(\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^{10}}\right)\)

\(-\frac{1}{2}A=\frac{1}{2^{11}}-\frac{1}{2}\)

BAN TU LAM NOT NHE

Ta có:

\(A=\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{10}}\)

\(\Leftrightarrow\)\(2A=1+\frac{1}{2}+...+\frac{1}{2^9}\)

\(\Leftrightarrow\)\(2A-A=A=\left(1+\frac{1}{2}+...+\frac{1}{2^9}\right)-\left(\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{10}}\right)\)

\(\Leftrightarrow\)\(=\)\(1+\frac{1}{2}+...+\frac{1}{2^9}-\frac{1}{2}-\frac{1}{2^2}-...-\frac{1}{2^{10}}\)

\(\Leftrightarrow\)\(=\)\(\left(1-\frac{1}{2^{10}}\right)+\left(\frac{1}{2}-\frac{1}{2}\right)+...+\left(\frac{1}{2^9}-\frac{1}{2^9}\right)\)

\(\Leftrightarrow\)\(=\)\(1-\frac{1}{2^{10}}\)

\(\Leftrightarrow\)\(=\)\(1-\frac{1}{1024}\)

\(\Leftrightarrow\)\(=\)\(\frac{1023}{1024}\)

\(\Leftrightarrow\)Vậy \(A=\frac{1023}{1024}\)

TL

2:_=10

   _=2:10

  _=1/5 hoặc 0,2 nha

mà lớp 2 làm j đã học phân số và số thập phân

HT

LÀ 500 NHÉ HT

TL

100 LÀ SỐ BÉ NHẤT CHIA hết cho 20;25 

nha

HT

\(y+y:\frac{12}{5}=\frac{9}{4}\)

\(y+y\times\frac{5}{12}=\frac{9}{4}\)

\(y\times\left(1+\frac{5}{12}\right)=\frac{9}{4}\)

\(y\times\frac{17}{12}=\frac{9}{4}\)

\(y=\frac{9}{4}:\frac{17}{12}\)

\(y=\frac{27}{17}\)

`Answer:`

`a)x+3/7=\frac{-5}{14}`

`<=>x=\frac{-5}{14}-3/7`

`<=>x=\frac{-11}{14}`

`b)1/2(x-4/5)=5/4`

`<=>x-4/5=5/4:1/2`

`<=>x=5/2+4/5`

`<=>x=\frac{33}{10}`

`c)|x-|\frac{4}{21}|}=3/7`

`=>x-\frac{4}{21}=3/7` hoặc `x-\frac{4}{21}=-3/7`

`=>x=\frac{13}{21}` hoặc `x=\frac{-5}21}`

bằng 500

TL

=10000:100+400

=100+400

=500

nha

HT

lên google mà hỏi 

nhưng k đấy