x - 18 - 42 = 23 - 43 - 70 - x

\(\rightarrow\) 2x = -30

\(\rightarrow\) x = -15

\(\left(-\left(x+15\right)\right)^2\) - 19 = \(3^2\) .5

\(\rightarrow\)\(x^2+30x+225\) - 19 = 45

\(\rightarrow x^2+30x+161=0\)

\(\rightarrow x^2+23x+7x+161=0\)

\(\rightarrow x\left(x+23\right)+7\left(x+23\right)=0\)

\(\rightarrow\left(x+7\right)\left(x+23\right)=0\)

\(\rightarrow\) x = -7 hoặc x = -23

Nhớ quy tắc:

x : y = ...

=> y = x: ...

=> x = ... nhân y

Tương tự áp dụng với cách làm suy ra:

y = 2/ 15 : (8/5 - 2/5)

\(\dfrac{2}{15}:y=\dfrac{8}{5}-\dfrac{2}{5}\)

\(\dfrac{2}{15}:y=\dfrac{6}{5}\)

\(y=\dfrac{2}{15}:\dfrac{6}{5}\)

\(y=\dfrac{2}{15}\times\dfrac{5}{6}\)

\(y=\dfrac{1}{9}\)

\(\dfrac{2}{15}:y=\dfrac{8}{5}-\dfrac{2}{5}\)

\(\dfrac{2}{15}:y=\dfrac{6}{5}\)

\(y=\dfrac{2}{15}:\dfrac{6}{5}\)

\(y=\dfrac{90}{10}=9\)

tính nhanh hay th bn?

99/2 x 3/5 + 3/5 x 103/2 - 3/5 

= 99/2 x 3/5 + 3/5 x 103/2 - 3/5 x 1

= 3/5 x (99/2 + 103/2 - 1)
= 3/5 x 100

= 60

99/2 x 3/5 + 3/5 x 103/2 - 3/5 

= 99/2 x 3/5 + 3/5 x 103/2 - 3/5 x 1

= 3/5 x (99/2 + 103/2 - 1)
= 3/5 x 100

= 60

Vậy ...

<=> 2x + 3 - 8 + 2x = 5 hoặc -2x - 3 + 8 - 2x = 5 

<=> 4x - 5 = 5 hoặc -4x + 5 = 5 

<=> 4x = 10 hoặc -4x = 0 

<=> x = 5 / 2 hoặc x = 0   

\(=\left(\dfrac{3+8}{12}\right)\cdot\dfrac{4}{5}=\dfrac{11}{12}\cdot\dfrac{4}{5}=\dfrac{44}{60}=\dfrac{11}{15}\)

x:5/3=9/5+2/5

x:5/3=11/5

x=11/5.5/3

x=11/3

x : 5/3 = 9/5 - 2/5

x : 5/3 = 7/5

x = 7/5 x 5/3

x = 7/3

\(x:\dfrac{5}{3}+\dfrac{2}{5}=\dfrac{9}{5}\)

\(x:\dfrac{5}{3}=\dfrac{9}{5}-\dfrac{2}{5}\)

\(x:\dfrac{5}{3}=\dfrac{7}{5}\)

\(x=\dfrac{7}{5}\times\dfrac{5}{3}\)

\(x=\dfrac{35}{15}=\dfrac{7}{3}\)

Để A là số nguyên thì x-5+7 chia hết cho x-5

=>x-5 thuộc {1;-1;7;-7}

=>x thuộc {6;4;12;-2}

\(\Leftrightarrow\left[3x+6-23\right]\cdot\left(9-8+20\cdot0\right)=147\)

=>3x=164

hay x=164/3

Giải:

B=1,4 .15/49 - (4/5+2/3) :2 1/5

B=7/5.15/49 - 22/15 : 11/5

B=3/7 - 2/3

B=-5/21

Chúc bạn học tốt!