G)\(\dfrac{x}{4}=\dfrac{1}{x}\)

\(\Rightarrow x.x=4.1\)

\(\Rightarrow x^2=4\)

Mà 4=\(2^2\)

Vậy x=2

ta có:

    \(105=3.5.7\)

    \(175=5^2.7\)

\(\)  ƯCLN(105,179)=5.7=35

hãy CMR :

     20 triệu + ngoài đường = cái nịt

\(A=\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}+\cdot\cdot\cdot+\dfrac{1}{120}\)

\(A=\dfrac{2}{2}\left(\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}+\cdot\cdot\cdot+\dfrac{1}{120}\right)\)

\(A=\dfrac{2}{1}\left(\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\cdot\cdot\cdot+\dfrac{1}{240}\right)\)

\(A=2\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\cdot\cdot\cdot+\dfrac{1}{15.16}\right)\)

\(A=2\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\cdot\cdot\cdot+\dfrac{1}{15}-\dfrac{1}{16}\right)\)

\(A=2\left(\dfrac{1}{4}-\dfrac{1}{16}\right)\)

\(A=2\left(\dfrac{4}{16}-\dfrac{1}{16}\right)\)

\(A=2.\dfrac{3}{16}\)

\(A=\dfrac{3}{8}\)

gọi d là ước chung của n-5 và n-2 (d thuộc Z)

       \(n-5⋮d\)

      \(n-2⋮d\)

\(\Rightarrow\left(n-2\right)-\left(n-5\right)\)\(⋮d\)

\(\Rightarrow n-2-n+5⋮d\)

\(\Rightarrow3⋮d\)

Đề thì như sai 

SAI

CÁC BẠN CHƠI CỎ MỸ À CÓ LỖI Đ ĐÂU

\(A=\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\cdot\cdot\cdot+\dfrac{1}{24.25}\)

\(A=\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\cdot\cdot\cdot+\dfrac{1}{24}-\dfrac{1}{25}\)

\(A=\dfrac{1}{5}-\dfrac{1}{25}\)

\(A=\dfrac{5}{25}-\dfrac{1}{25}\)

\(A=\dfrac{4}{25}\)

\(B=\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+\cdot\cdot\cdot+\dfrac{2}{99.101}\)

\(B=\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\cdot\cdot\cdot+\dfrac{1}{99}-\dfrac{1}{101}\)

\(B=\dfrac{1}{1}-\dfrac{1}{101}\)

\(B=\dfrac{101}{101}-\dfrac{1}{101}\)

\(B=\dfrac{100}{101}\)