D

D

D

a) \(\dfrac{5}{7}\times\dfrac{5}{9}+\dfrac{4}{9}\times\dfrac{5}{7}\)

\(=\dfrac{5}{7}\times\left(\dfrac{4}{9}+\dfrac{5}{9}\right)\)

\(=\dfrac{5}{7}\times1\)

\(=\dfrac{5}{7}\)

b) \(\dfrac{1}{10}+\dfrac{5}{9}+\dfrac{4}{9}+\dfrac{9}{10}-1\)

\(=\left(\dfrac{5}{9}+\dfrac{4}{9}\right)+\left(\dfrac{1}{10}+\dfrac{9}{10}-1\right)\)

\(=1+0\)

\(=1\)

c) \(\dfrac{5}{7}\times\dfrac{5}{9}+\dfrac{4}{9}\times\dfrac{5}{7}+\dfrac{2}{7}\)

\(=\dfrac{5}{7}\times\left(\dfrac{5}{9}+\dfrac{4}{9}\right)+\dfrac{2}{7}\)

\(=\dfrac{5}{7}+\dfrac{2}{7}\)

\(=1\)

d) \(\dfrac{2}{7}+\dfrac{2}{8}+\dfrac{1}{4}+\dfrac{1}{7}+\dfrac{4}{7}\)

\(=\left(\dfrac{2}{8}+\dfrac{1}{4}\right)+\left(\dfrac{2}{7}+\dfrac{1}{7}+\dfrac{4}{7}\right)\)

\(=\left(\dfrac{1}{4}+\dfrac{1}{4}\right)+1\)

\(=\dfrac{1}{2}+1\)

\(=\dfrac{3}{2}\)

e) \(\dfrac{4}{5}+\dfrac{3}{10}+\dfrac{2}{10}+0,7\)

\(=\dfrac{4}{5}+\dfrac{5}{10}+\dfrac{7}{10}\)

\(=\dfrac{4}{5}+\dfrac{12}{10}\)

\(=\dfrac{4}{5}+\dfrac{6}{5}\)

\(=\dfrac{10}{5}\)

\(=2\)

g) \(362\times728+326\times272\)

\(=326\times\left(728+272\right)\)

\(=326\times1000\)

\(=326000\) 

Ai giải hộ e với e phải đi học

a. 8 + (x - 9) = 125 - 64

8 + (x - 9) = 61

x - 9 = 53

x = 62

b. 5 x (X + 7) - 10 = 8 x 5

5 x (X + 7) - 10 = 40

5 x (X + 7) = 50

X + 7 = 10

X = 3

a) {[( 3² + 1 ) . 10 - ( 8 : 2 + 6 ) ] : 2 } + 55 -( 10 : 5 )³

=  (        10   . 10 -      10           : 2 ) + 55 -      6

=                      90                    : 2 ) +  55  -  6

=                              45          +           55 -  6

=                                  100       -      6

=                                        94

b) 100 - [ 60 - ( 9 - 2 )² ] . 3²

=  100 - [ 60 -    7²   ] . 9

=  100 - [ 60 -  49 ] . 9

=  100 -      11        . 9

=  100        -     99

=             1

c) [ ( 125³ )  . 7⁵ - ( 175 )⁵ : 5 ] : 2016²⁰¹⁷

=                  0                        : 2016²⁰¹⁷

=     0

+  bài d kg hiểu! Xin lỗi

9 x 2 = 18

9 x 5 = 45

9 x 8 = 72

9 x 10 = 90

2 x 9 = 18

5 x 9 = 45

8 x 9 = 72

10 x 9 = 90

Khó quá

thế mới hỏi

( 2x² + 3x - 1² ) - 5.(2x² + 3x + 3) + 24 = 0

Đặt 2x² + 3x - 1 = a

 \(\Rightarrow\)2x² + 3x + 3 = a + 4

Khi đó phương trình trở thành :

 a  - 5.(a + 4 ) + 24 = 0

\(\Leftrightarrow\)a - 5a - 20 + 24 = 0

\(\Leftrightarrow\) -4a + 4 = 0

\(\Leftrightarrow\) -4a = -4

\(\Leftrightarrow\)a = 1

Với a = 1

\(\Rightarrow\)2x² + 3x - 1 = 1

\(\Leftrightarrow\)2x² + 3x  - 2 = 0

\(\Leftrightarrow\)2x² + 4x - x - 2 = 0

\(\Leftrightarrow\)2x.( x + 2 ) - ( x + 2 ) = 0

\(\Leftrightarrow\)( 2x - 1 ).( x + 2) = 0

\(\Leftrightarrow\)\(\orbr{\begin{cases}2x-1=0\\x+2=0\end{cases}}\)\(\Leftrightarrow\)\(\orbr{\begin{cases}x=\frac{1}{2}\\x=-2\end{cases}}\)

Vậy phương trình có nghiệm là : x = \(\frac{1}{2}\), x = -2

a: \(\dfrac{x-1}{x^2-x+1}-\dfrac{x+1}{x^2+x+1}=\dfrac{10}{x\left(x^4+x^2+1\right)}\)

\(\Leftrightarrow x\left(x-1\right)\left(x^2+x+1\right)-x\left(x+1\right)\left(x^2-x+1\right)=10\)

\(\Leftrightarrow x\left(x^3-1\right)-x\left(x^3+1\right)=10\)

=>-2x=10

hay x=-5

d: \(\Leftrightarrow\dfrac{1}{\left(x+1\right)\left(x+2\right)}+\dfrac{1}{\left(x+2\right)\left(x+3\right)}+...+\dfrac{1}{\left(x+7\right)\left(x+8\right)}=\dfrac{1}{14}\)

\(\Leftrightarrow\dfrac{1}{x+1}-\dfrac{1}{x+8}=\dfrac{1}{14}\)

\(\Leftrightarrow\left(x+1\right)\left(x+8\right)=14\left(x+8\right)-14\left(x+1\right)\)

\(\Leftrightarrow x^2+9x+8=14x+112-14x-14=98\)

\(\Leftrightarrow x^2+9x-90=0\)

\(\Leftrightarrow x\in\left\{6;-15\right\}\)

1) 5 ( x + 7 ) - 10 = 50 => 5 ( x + 7 ) = 60 

=>  x + 7 =12 

=> x = 12 - 7 

=> x = 5

2) 42 : x - 5 = 1

=> 42 : x = 6

=> x = 7

3) ( x-1 ) ( x- 4 ) = 5

=> x = - 0,1925.....

4) 7x + 8x - 5x = 70

=> 10x = 70

=> x = 7

5) 4x + 9x - x = 60

=> 12x = 60 

=> x = 5

*)5(x+7)-10=50

5(x+7)=60

x+7=12

x=5

*)42:x-5=1

42:x=6

x=7

*)7x+8-5x=70

x(7+8-5)=70

10x=70

x=7

*)4x+9x-x=60

x(4+9-1)=60

12x=60

x=5

a, \(\dfrac{x}{-15}=\dfrac{-60}{3}\)

=> x= \(\dfrac{-60.-15}{3}=300\)

b, \(\dfrac{10}{x}=\dfrac{-30}{-60}\)

=> x= \(\dfrac{10.-60}{-30}=20\)

c, \(\dfrac{5}{3}=\dfrac{x}{9}\)

=> \(x=\dfrac{5.9}{3}=15\)

A, x/-15= - 60/3

=> x.3 = -15.(-60)

x.3 = 900

x = 900 : 3

x = 300

Vậy x = 300

B, 10/x = -30/-60

=> x.(-30) = 10.(-60)

x.(-30) = -600

x = -600 : (-30)

x = 20

Vậy x = 20

C, 5/3 = x/9

=> 5.9 = 3.x

45 = 3.x

3.x = 45

x = 45 : 3

x = 15

Vậy x = 15