Phương pháp giải:

Muốn tìm số bị trừ ta lấy hiệu cộng với số trừ.

Lời giải chi tiết:

a) x − 3 = 9

    x = 9 + 3

    x = 12

b) x − 8 = 16

    x = 16 + 8

    x = 24

c) x − 20 = 35

    x = 35 + 20

    x = 55

d) x − 5 = 17

    x = 17 + 5

    x = 22

e) x − 15 = 27

    x = 27 + 15

    x = 42

g) x − 36 = 36

    x = 36 + 36

    x = 72

(-5)+(-11)

\(\left(x-1\right)\left(x-4\right)\left(x-5\right)\left(x-8\right)+36=0\)

\(\left[\left(x-1\right)\left(x-8\right)\right]\left[\left(x-4\right)\left(x-5\right)\right]+36=0\)

\(\left(x^2-9x+8\right)\left(x^2-9x+20\right)+36=0\)

Đặt \(a=x^2-9x+14\)ta có :

\(\left(a-6\right)\left(a+6\right)+36=0\)

\(a^2-6^2+36=0\)

\(a^2=0\)

Thay \(a=x^2-9x+14\)ta có :

\(\left(x^2-9x+14\right)^2=0\)

\(\Leftrightarrow x^2-9x+14=0\)

\(\Leftrightarrow x^2-2x-7x+14=0\)

\(\Leftrightarrow x\left(x-2\right)-7\left(x-2\right)=0\)

\(\Leftrightarrow\left(x-2\right)\left(x-7\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-2=0\\x-7=0\end{cases}\Rightarrow\orbr{\begin{cases}x=2\\x=7\end{cases}}}\)

Vậy,...........

\(\left(x-1\right)\left(x-4\right)\left(x-5\right)\left(x-8\right)+36=0\)

\(\left(x-1\right)\left(x-8\right)\left(x-4\right)\left(x-5\right)+36=0\)

\(\left(x^2-9x+8\right)\left(x^2-9x+20\right)+36=0\)

Đặt \(x^2-9x+14=t\)

\(\left(t-6\right)\left(t+6\right)+36=0\)

\(t^2-36+36=0\)

\(\Rightarrow t^2=0\)

\(\Rightarrow x^2-9x+16=0\)

\(\Rightarrow x^2-2.\frac{9}{2}x+\frac{81}{4}=\frac{17}{4}\)

\(\Rightarrow\left(x-\frac{9}{2}\right)^2=\frac{17}{4}\)

\(\Rightarrow x=\hept{\begin{cases}\sqrt{\frac{17}{4}}+\frac{9}{2}\\-\sqrt{\frac{17}{4}}+\frac{9}{2}\end{cases}}\)

Có: \(\dfrac{x}{8}=\dfrac{y}{5}\) và \(x+2y=-36\) (1)

Áp dụng tính chất của dãy tỉ số bằng nhau và (1), ta được:

\(\dfrac{x}{8}=\dfrac{y}{5}=\dfrac{2y}{10}=\dfrac{x+2y}{8+10}=\dfrac{-36}{18}=-2\)

\(\Rightarrow\left\{{}\begin{matrix}x=-2\cdot8=-16\\y=-2\cdot5=-10\end{matrix}\right.\)

Theo mình đây là Toán lớp 7 chứ nhỉ?

\(\frac{x}{-4}=\frac{-16}{x}\)

\(\Rightarrow x\cdot x=-16\cdot\left(-4\right)\)

\(\Rightarrow x^2=64\)

\(\Rightarrow x^2=\left(\pm8\right)^2\)

\(\Rightarrow x=\pm8\)

a)\(\left(x-\frac{5}{8}\right).\frac{5}{18}=-\frac{15}{36}\)

\(\Rightarrow x-\frac{5}{8}=\frac{-15}{36}.\frac{18}{5}\)

\(\Rightarrow x-\frac{5}{8}=-\frac{3}{2}\)

\(\Rightarrow x=-\frac{12}{8}+\frac{5}{8}=-\frac{7}{8}\)

b)\(\frac{x}{-4}=\frac{-16}{x}\)

\(\Rightarrow x^2=64\)

\(\Rightarrow x=\orbr{\begin{cases}8\\-8\end{cases}}\)

\(\left(x-\frac{5}{8}\right)\frac{5}{18}=-\frac{15}{36}\)

\(\Leftrightarrow\frac{5}{18}x-\frac{25}{144}=-\frac{15}{36}\)

\(\Leftrightarrow\frac{5}{18}x=-\frac{35}{144}\)

\(\Leftrightarrow x=-\frac{7}{8}\)

A/ X= \(-\frac{7}{8}\)

B/ X= \(\frac{7}{6}\)

`(5/6 -x+7/12) : ( 11/24 -1/8)=11/36`

`=>(5/6 -x+7/12) : (11/24 - 3/24)=11/36`

`=>(5/6 -x+7/12) : 8=11/36`

`=>5/6 -x+7/12=11/36 xx 8`

`=>5/6 -x+7/12=22/9`

`=> x+7/12=5/6-22/9`

`=> x+7/12=-29/18`

`=>x=-29/18 -7/12`

`=>x=-79/36`

79/36 nhé

x . 5 + 122 + 236 = 633

x . 5 + 358 = 633

x . 5 = 633 - 358

x . 5 = 275

x = 275 : 5

x = 55

b) (x : 12) . 7 + 8 = 36

(x : 12) . 7 = 36 - 8

(x : 12) . 7 = 28

x : 12 = 28 : 7

x : 12 = 4

x = 4 . 12

x = 48

#Học tốt!!!

X x 5 + 122 + 236 = 633

X x 5 + 122 = 633 - 236 

X x 5 + 122 = 397

X x 5 = 397 - 122

X x 5 = 275

X = 275 : 5 

X = 55

(X : 12) x 7 + 8 = 36

(X : 12) x 7 = 36 - 8

(X : 12) x 7 = 28

X : 12 = 28 : 7

X : 12 = 4

X = 12 : 4

X = 3

lộn 12 x 4

= 48

từ 1 đến 996 có 996 chữ số nếu chia thành 4 số 1 cặp thì có 249 cặp

x[(1+2-3-4)+(5+6-7-8)+...+(993+994-995-996)+997]=36

x.[(-4).249+997]=36

x.1=36

x=36:1

x=36

từ 1 đến 996 có 996 chữ số nếu chia thành 4 số 1 cặp thì có 249 cặp

x[(1+2-3-4)+(5+6-7-8)+...+(993+994-995-996)+997]=36

x.[(-4).249+997]=36

x.1=36

x=36:1

x=36

\(a,\left(x-\dfrac{5}{8}\right)\cdot\dfrac{8}{18}=-\dfrac{15}{16}\\ x-\dfrac{5}{8}=-\dfrac{15}{36}:\dfrac{8}{18}\\ x-\dfrac{5}{8}=-\dfrac{15}{16}\\ x=-\dfrac{15}{16}+\dfrac{5}{8}\\ x=-\dfrac{15}{16}+\dfrac{10}{16}\\ x=-\dfrac{5}{16}\\ b,x-\dfrac{1}{3}=\dfrac{5}{6}\\ x=\dfrac{5}{6}+\dfrac{1}{3}\\ x=\dfrac{5}{6}+\dfrac{2}{6}\\ x=\dfrac{7}{6}\)

\(a,\left(x-\dfrac{5}{8}\right).\dfrac{5}{8}=-\dfrac{15}{36}\)

\(\left(x-\dfrac{5}{8}\right)=-\dfrac{15}{36}\div\dfrac{5}{8}\)

\(x-\dfrac{5}{8}=-\dfrac{2}{3}\)

\(x=-\dfrac{2}{3}+\dfrac{5}{8}\)

\(x=-\dfrac{1}{24}\)

\(b,\left(x-\dfrac{1}{3}\right)=\dfrac{5}{6}\)

\(\Rightarrow x-\dfrac{1}{3}=\dfrac{5}{6}\)

\(x=\dfrac{5}{6}+\dfrac{1}{3}\)

\(x=\dfrac{7}{6}\)

\(a)\left(x-\dfrac{5}{8}\right).\dfrac{5}{18}=-\dfrac{15}{36}\)

    \(\left(x-\dfrac{5}{8}\right).\dfrac{5}{18}=\dfrac{-5}{12}\) 

     \(\left(x-\dfrac{5}{8}\right)\)       \(=\dfrac{-5}{12}\div\dfrac{5}{18}=\dfrac{-3}{2}\)

        \(x\)                 \(=\left(\dfrac{-3}{2}\right)+\dfrac{5}{8}=\dfrac{-7}{8}\)

\(b)\left(x-\dfrac{1}{3}\right)=\dfrac{5}{6}\)

      \(x\)            \(=\dfrac{5}{6}+\dfrac{1}{3}\)

      \(x\)            \(=\dfrac{7}{6}\)

a. 37-7.(x+1)=40-8.3

37 - 7(x+1) = 16 

7(x+1) = 21

x+1 = 3

x=2

b. (x+5).3=11=10+(3+4).4

(sao có 2 dấu bằng, dấu nào là dấu cộng do viết nhầm ???)

c. 25-5.3+4.10=100-5.x

50 = 100 - 5x 

5x = 50

x=10

d. 36+2.(x-7)=12+8.(3+5)-36

36 + 2(x-7) = 40

2(x-7) = 4

x-7 =2

x=9

e. 3.(x+7)-9=11.5-5-8

3(x+7) - 9 = 42 

3(x+7) = 51

x+7 = 17 

x=10