`3 m 45cm = …3,45.m`

`5,9m = 9…m…90.cm`

`5 km 34 m = …5,034km`

`4567 m = …4,567.km`

`2,67 km = 2670…m`

`4,6 km =4…km…600.m`

`Oa` nằm giữa các tia :

`Of` và `Od`

`Of` và `Ob`

`Of` và `Oc`

:vvvvv box Toán thì nó là hộp toán hã =))? 

` 1,23; 1,32; 2,13; 2,31;3,12;3,21`

`a)`

\(\dfrac{23}{10}=2\dfrac{3}{10}=2,3\)

\(\dfrac{47}{10}=4\dfrac{7}{10}=4,7\)

\(\dfrac{137}{100}=1\dfrac{37}{100}=1,37\)

\(\dfrac{123}{10}=10\dfrac{23}{10}=12,3\)

\(\dfrac{6789}{100}=67\dfrac{89}{100}=67,89\)

`b)`

`45% = 45/100 = 9/20`

`70% = 70/100 = 7/10`

`25% = 25/100 = 1/4`

Câu `1:`

\(a)\\ x^2-7\\ =\left(x-\sqrt{7}\right)\left(x+\sqrt{7}\right)\\ b)\\ x^2-2\sqrt{2}x+2\\ =x^2-2\sqrt{2}x+\left(\sqrt{2}\right)^2\\ =\left(x-\sqrt{2}\right)^2\\ c)\\ x^2+2\sqrt{13}x+13\\ =x^2+2\sqrt{13}x+\left(\sqrt{13}\right)^2\\ =\left(x-\sqrt{13}\right)^2\)

\(\dfrac{2}{5}+\dfrac{10}{20}:\dfrac{2}{3}\\ =\dfrac{2}{5}+\dfrac{1}{2}:\dfrac{2}{3}\\ =\dfrac{2}{5}+\dfrac{1\times3}{2\times2}\\ =\dfrac{2}{5}+\dfrac{3}{4}\\ =\dfrac{23}{20}\)

`b)`

`x/24 = 5/12 + 1/3`

`x/24 = 3/4`

`x = 3/4 xx 24`

`x = 18`

`c)`

`x/4 = 1/2`

`x = 1/2 xx 4`

`x = 2`

`e)`

`x/15 + 7/20 = 73/60`

`x/15 = 73/60 - 7/20`

`x/15 = 13/15`

`x = 13/15 xx 15`

`x= 13`

`f)`

`(x+1)/3 = 25/(-5)`

`(x+1)/3 = -5`

`x + 1 = (-5) xx 3`

`x + 1 = -15`

`x = -15 - 1`

`x = -16`

\(g,\dfrac{11}{8}+\dfrac{13}{6}=\dfrac{85}{x}\\ \Rightarrow\dfrac{85}{24}=\dfrac{85}{x}\\ \Leftrightarrow x=24\\ k,-\dfrac{7}{x}+\dfrac{8}{15}=-\dfrac{1}{20}\\ \Rightarrow-\dfrac{7}{x}=-\dfrac{7}{12}\\ \Leftrightarrow x=12\)

\(m,\dfrac{x+\left(-2\right)}{5}=\dfrac{-12}{15}\\ \Leftrightarrow15\left(x+\left(-2\right)\right)=5\cdot\left(-12\right)\\ \Leftrightarrow x=-2\\ n,\dfrac{x-1}{-5}=\dfrac{12}{20}\\ \Leftrightarrow20\left(x-1\right)=\left(-5\right)\cdot12\\ \Leftrightarrow x=-2\)

\(p,\dfrac{7}{12}+\dfrac{x}{15}=\dfrac{1}{20}\\ \Rightarrow\dfrac{x}{15}=-\dfrac{8}{15}\\ \Leftrightarrow x=-8\)