\(=\dfrac{4}{25}+\dfrac{1}{2}\left(\dfrac{9}{2}-2\right)-\dfrac{1}{4}=\dfrac{4}{25}+\dfrac{1}{2}\left(\dfrac{5}{2}\right)-\dfrac{1}{4}=\dfrac{4}{25}+\dfrac{5}{4}-\dfrac{1}{4}=\dfrac{4}{25}+1=\dfrac{29}{25}\)

`(-2/5)^2 + 1/2 . (4,5 - 2) - 25%`

`=4/25 + 1/2 . (9/2 - 2) - 1/4`

`=4/25 + 1/2 . (9/2 - 4/2)-1/4`

`=4/25 + 1/2 . 5/2 - 1/4`

`=4/25 + 5/4 - 1/4`

`=4/25 + 1`

`=4/25  + 25/25`

`=29/25`

a] 425 . 7 . 4 - 170 . 60

= ( 425 . 4 ) - ( 7 .170 ) . 60

= 1700 - 1190 . 60

= 510 . 60

= 30600

a] 425 . 7 .4 - 170 . 60

= ( 425 . 4 ) . 7 - ( 170 . 10 ) . 6

= 1700 . 7 - 1700 . 6

= 1700 . ( 7-6 )

= 1700 . 1

= 1700 

a] 17 . 82 + 19 . 17 - 17

= 17 . 82 + 19 . 17 - 17.1

= 17 . ( 82 + 19  - 1 )

= 17 . 100

= 1 700 

a] 17 . 82 + 19 . 17 - 17

= 17 . ( 82 + 19 - 17 )

= 17 . 84

= 1428

a, \(A=\left(2011-1\right)\left(2011+1\right)=2011^2-1< B\)

b, \(C=\left(2012-2\right)\left(2012+2\right)=2012^2-4< D\)

.

a] 28 . 62 - 28 . 57

= 28 . ( 62 - 57 )

= 28 . 5

= 140 

a] 28 . 62 - 28 . 57

= 28 . ( 62 - 57 )

= 28 . 5

= 140 

a, \(\left(x+1\right)\left(x+2\right)=1.12=2.6=3.4\)

TH1 \(\left\{{}\begin{matrix}x+1=1\\x+2=12\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=0\\x=10\end{matrix}\right.\)

TH2 \(\left\{{}\begin{matrix}x+1=2\\x+2=6\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\x=4\end{matrix}\right.\)

TH3 : \(\left\{{}\begin{matrix}x+1=3\\x+2=4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\x=2\end{matrix}\right.\)

b, \(x^2+x-12=0\Leftrightarrow\left(x+4\right)\left(x-3\right)=0\Leftrightarrow\left[{}\begin{matrix}x=-4\\x=3\end{matrix}\right.\)

c, \(\dfrac{x+5}{x}=1+\dfrac{5}{x}\Rightarrow x\inƯ\left(5\right)=\left\{\pm1;\pm5\right\}\)

3, tính :

a) 1/1.2 + 1/3.4 + ... + 1/98.99 + 1/99.100

=  \(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+....+\dfrac{1}{98}-\dfrac{1}{99}+\dfrac{1}{99}-\dfrac{1}{100}\)

= \(1-\dfrac{1}{100}\)

= \(\dfrac{99}{100}\)

b, 3/1.4 + 3/4.7 + ... + 3/88.91 + 3/91.94

= \(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{88}-\dfrac{1}{91}+\dfrac{1}{91}-\dfrac{1}{94}\)

= \(1-\dfrac{1}{94}\)

= \(\)\(\dfrac{93}{94}\)

 c, 1/5 + 1/50 + 1/150 + 1/300 + 1/500

= 300/1500 + 30/1500 + 10/1500 + 5/1500 +3/1500

= 29/125

 2 . 14 . 47 + 7 . 53 . 4

= 2 .2.7  . 47 + 7 . 53 . 2.2 

=  2.2.7 . ( 47 + 53 )

= 2.2.7 . 100

= 4.7.100

= 28.100

= 2800

 2 . 14 . 47 + 7 . 53 . 4

= 2 .2.7  . 47 + 7 . 53 . 2.2 

=  2.2.7 . ( 47 + 53 )

= 2.2.7 . 100

= 4.7.100

= 28.100

= 2800

( 25/14 + 3 . 13/42 ) : 3/7

= ( 25/14 + 13/14 ) : 3/7

= 19/7 : 3/7

= 19/3 

7/9 + 5/9 . 11/23 + 5/9 .12 / 23

= 7/9 + 5/9 . ( 11/23 + 12/23 )

= 7/9 + 5/9 . 1

= 7/9 + 5/9

= 4/3 

=(25/14 + 13/14) : 3/7 = 3/7 : 19/7 = 3/19

= 7/9 + 5/9( 11/23+12/23) =7/9 +5/9.1 =7/9+5/9=4/3

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