a: =>x=-7/6+5/8=-13/24

b: =>x=-14/25-3/4=-131/100

c: \(x=\dfrac{-33}{26}:\dfrac{-9}{13}=\dfrac{33}{26}\cdot\dfrac{13}{9}=\dfrac{11}{3}\cdot\dfrac{1}{2}=\dfrac{11}{6}\)

d: \(x=\dfrac{4}{9}:\dfrac{5}{3}=\dfrac{4}{9}\cdot\dfrac{3}{5}=\dfrac{12}{45}=\dfrac{4}{15}\)

Học sinh nhẩm và ghi:

8 x 5 = 40

8 x 4 = 32

8 x 6 = 48

8 x 3 = 24

40 : 8 = 5

32 : 8 = 4

48 : 8 = 6

24 : 8 = 3

40 : 5 = 8

32 : 4 = 8

48 : 6 = 8

24 : 3 = 8

(chú ý: mối quan hệ giữa nhân và chia)

Tính nhẩm:

8 x 5 = 40

8 x 4 = 32

8 x 6 = 48

8 x 3 = 24

40 : 8 = 5

32 : 8 = 4

48 : 8 = 6

24 : 8 = 3

40 : 5 = 8

32 : 4 = 8

48 : 6 = 8

24 : 3 = 8

k cho mik với

`a, (4x+5) : 3 -121:11=14`

`=> (4x+5) : 3 - 11=14`

`=> (4x+5) : 3 =14+11`

`=> (4x+5) : 3 = 25`

`=> 4x+5=25xx3`

`=>4x+5= 75`

`=> 4x=75-5`

`=>4x=70`

`=>x= 70/4`

`=>x= 35/2`

`b, 2+4+6+...+x=2450`

Số lượng của dãy là :

`(x-2)/2 + 1= (x-2)/2 +2/2= x/2`

Tổng số lượng là :

\(\dfrac{\left(x+2\right)\cdot\dfrac{x}{2}}{2}=\dfrac{\dfrac{x^2}{2}+\dfrac{2x}{2}}{2}=\dfrac{x\left(x+2\right)}{4}\)

\(\dfrac{x\left(x+2\right)}{4}=2450\)

\(\Rightarrow x\left(x+2\right)=2450\cdot4\\ \Rightarrow x\left(x+2\right)=9800\)

`=>x=98`

`c,` `1` nhân `32` sao?

`d, 2x+3x=1505`

`=> (2+3)x=1505`

`=> 5x=1505`

`=> x= 1505:5`

`=>x= 301`

a) 3/7 + 3/4 - 1/2 =33/28-1/2=19/28

b) 6/11 + 2/9 x 12 =6/11+8/3=106/33

c) 5/7 - 8/5 : 4 =5/7-2/5=11/35

a) 3/7 + 3/4 - 1/2 = \(\dfrac{12}{28}+\dfrac{21}{28}-\dfrac{14}{28}=\dfrac{19}{28}\)

b) 6/11 + 2/9 x 12 = \(\dfrac{6}{11}+\dfrac{8}{3}=\dfrac{18}{33}+\dfrac{88}{33}=\dfrac{106}{33}\)

c) 5/7 - 8/5 : 4 = \(\dfrac{5}{7}-\dfrac{2}{5}=\dfrac{25}{35}-\dfrac{14}{35}=\dfrac{11}{35}\)

3/7 + 3/4 - 1/2 = 33/28 - 1/2 = 19/28

6/11 + 2/9 x 12 = 6/11+ 8/3 = 106/33

5/7 - 8/5 : 4 = 5/7 - 2/5 = 11/35

`@` `\text {Ans}`

`\downarrow`

`1,`

`a)`

`-7/25 + (-8)/25`

`= (-7 - 8)/25`

`= -15/25`

`= -3/5`

`b)`

`6/13 + (-15)/39`

`= 18/39 + (-15)/39`

`= (18 - 15)/39`

`= 3/39`

`= 1/13`

`c)`

`5/7 + 4/(-14)`

`= 10/14 + (-4)/14`

`= (10 - 4)/14`

`= 6/14`

`= 3/7`

`d)`

`-8/18 + (-15)/27`

`= -4/9 + (-5)/9`

`= (-4-5)/9`

`= -9/9 = -1`

`2,`

`a)`

`3/5 + (-7)/4`

`= 12/20 + (-35)/20`

`= (12 - 35)/20`

`=-23/20`

`b)`

`(-2) + (-5)/8`

`= (-16)/8 + (-5)/8`

`= (-16 - 5)/8`

`= -21/8`

`c)`

`1/8 + (-5)/9`

`= 9/72 + (-40)/72`

`= (9-40)/72`

`= -31/72`

`d)`

`6/13 + (-14)/39`

`= 18/39 + (-14)/39`

`= (18 - 14)/39`

`= 4/39`

`e)`

`(-18)/24 + 15/21`

`= (-3)/4 + 5/7`

`= (-21)/28 + 20/28`

`= (-21 + 20)/28`

`= -1/28`

\(b,x-\dfrac{2}{5}=\dfrac{4}{13}\\ \Rightarrow x=\dfrac{4}{13}+\dfrac{2}{5}\\ \Rightarrow x=\dfrac{46}{65}\\ c,\dfrac{12}{7}-x=\dfrac{5}{8}\\ \Rightarrow x=\dfrac{12}{7}-\dfrac{5}{8}\\ \Rightarrow x=\dfrac{61}{56}\\ d,\dfrac{6}{11}+x=\dfrac{3}{2}\\ \Rightarrow x=\dfrac{3}{2}-\dfrac{6}{11}\\ \Rightarrow x=\dfrac{21}{22}\)

b, \(x=\dfrac{4}{13}+\dfrac{2}{5}=\dfrac{20+26}{5.13}=\dfrac{46}{65}\)

c, \(x=\dfrac{12}{7}-\dfrac{5}{8}=\dfrac{96-35}{56}=\dfrac{61}{56}\)

d, \(x=\dfrac{3}{2}-\dfrac{6}{11}=\dfrac{33-12}{22}=\dfrac{21}{22}\)

b: x-2/5=4/13

=>x=4/13+2/5=20/65+26/65=46/65

c: 12/7-x=5/8

=>x=12/7-5/8=96/56-35/56=61/56

d: 6/11+x=3/2

=>x=3/2-6/11=33/22-12/22=21/22

nhiều quá :((

\(a,2\left(x-5\right)-3\left(x+7\right)=14\)

\(2x-10-3x-21=14\)

\(-x-31=14\)

\(-x=45\)

\(x=45\)

\(b,5\left(x-6\right)-2\left(x+3\right)=12\)

\(5x-30-2x-6=12\)

\(3x-36==12\)

\(3x=48\)

\(x=16\)

\(c,3\left(x-4\right)-\left(8-x\right)=12\)

\(3x-12-8+x=0\)

\(4x-20=0\)

\(4x=20\)

\(x=5\)

Cố nốt nha bn ! 

cảm ơn, bn nha:)))

mà hình như bạn TOP 3 trả lời câu hỏi pải ko nhỉ???

d, \(-7\left(3x-5\right)+2\left(7x-14\right)=28\)

\(\Leftrightarrow-21x+35+14x-28=28\Leftrightarrow-7x=21\Leftrightarrow x=-3\)

e, \(5\left(3-2x\right)+5\left(x-4\right)=6-4x\)

\(\Leftrightarrow15-6x+5x-20=6-4x\Leftrightarrow-5-x=6-4x\)

\(\Leftrightarrow-11+3x=0\Leftrightarrow x=\frac{11}{3}\)

f, \(-5\left(2-x\right)+4\left(x-3\right)=10x-15\)

\(\Leftrightarrow-10+5x+4x-12=10x-15\Leftrightarrow-22+9x=10x-15\)

\(\Leftrightarrow-7-x=0\Leftrightarrow x=-7\)

Giải:

a) \(\left|48-3x\right|=0\)

\(\Leftrightarrow48-3x=0\)

\(\Leftrightarrow3x=48\)

\(\Leftrightarrow x=\dfrac{48}{3}=16\)

Vậy x = 16.

b) \(\left|-x-7\right|=24\)

\(\Leftrightarrow\left[{}\begin{matrix}-x-7=24\\-x-7=-24\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}-x=31\\-x=-17\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-31\\x=17\end{matrix}\right.\)

Vậy \(x=-31\) hoặc \(x=17\).

c) \(\left|4-x\right|=21\)

\(\Leftrightarrow\left[{}\begin{matrix}4-x=21\\4-x=-21\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-17\\x=25\end{matrix}\right.\)

Vậy \(x=-17\) hoặc \(x=25\).

d) \(\left|x+8\right|+12=0\)

\(\Leftrightarrow\left|x+8\right|=-12\)

\(\Leftrightarrow\left[{}\begin{matrix}x+8=-12\\x+8=-\left(-12\right)\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-20\\x=4\end{matrix}\right.\)

Vậy \(x=-20\) hoặc \(x=4\).

e) \(6-\left|x\right|=2\)

\(\Leftrightarrow\left|x\right|=6-2=4\)

\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)

Vậy \(x=4\) hoặc \(x=-4\).

Chúc bạn học tốt!

1. |48 - 3x| = 0.

\(\Leftrightarrow\) 48 - 3x = 0.

\(\Leftrightarrow\) 3x = 48.

\(\Leftrightarrow\) x = \(\dfrac{48}{3}=16.\)

Vậy x = 16.

2. |-x - 7| = 24.

\(\Leftrightarrow\left[{}\begin{matrix}-x-7=24.\\-x-7=-24.\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}-x=31.\\-x=-17.\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-31.\\x=17.\end{matrix}\right.\)

Vậy \(\left[{}\begin{matrix}x=-31.\\x=17.\end{matrix}\right.\)

3. |4 - x| = 21.

\(\Leftrightarrow\left[{}\begin{matrix}4-x=21.\\4-x=-21.\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-17.\\x=25.\end{matrix}\right.\)

Vậy \(\left[{}\begin{matrix}x=-17.\\x=25.\end{matrix}\right.\)

4. |x + 8| + 12 = 0.

|x + 8| = 0 - 12.

|x + 8| = -12.

\(\Leftrightarrow\left[{}\begin{matrix}x+8=-12.\\x+8=-\left(-12\right).\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x+8=-12.\\x+8=12.\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-20.\\x=4.\end{matrix}\right.\)

Vậy \(\left[{}\begin{matrix}x=-20.\\x=4.\end{matrix}\right.\)

5. 6 - |x| = 2.

|x| = 6 - 2.

|x| = 4.

\(\Leftrightarrow\left[{}\begin{matrix}x=4.\\x=-4.\end{matrix}\right.\)

Vậy \(\left[{}\begin{matrix}x=4.\\x=-4.\end{matrix}\right.\)

1. Ta có 2 trường hợp:

TH1: 48-3x=0 <=> 3x=48 <=> x=16

TH2:-48-3x=0

\(A=5\cdot4^{15}\cdot9^9-4\cdot3^{20}\cdot8^9\)

\(A=5\cdot\left(2^2\right)^{15}\cdot\left(3^2\right)^9-2^2\cdot3^{20}\cdot\left(2^3\right)^9\)

\(A=5\cdot2^{30}\cdot3^{18}-2^2\cdot3^{20}\cdot2^{27}\)

\(A=5\cdot2^{30}\cdot3^{18}-2^{29}\cdot3^{20}\)

\(A=2^{29}\cdot3^{18}\cdot\left(5\cdot2^1\cdot1-1\cdot3^2\right)\)

\(A=2^{29}\cdot3^{18}\cdot\left(5-9\right)\)

\(A=-2^2\cdot2^{29}\cdot3^{18}\)

\(A=-2^{31}\cdot3^{18}\)

_______________

\(B=5\cdot2^9\cdot6^{19}-7\cdot2^{29}\cdot27^6\)

\(B=5\cdot2^9\cdot2^{19}\cdot3^{19}-7\cdot2^{29}\cdot\left(3^3\right)^6\)

\(B=5\cdot2^{28}\cdot3^{19}-7\cdot2^{29}\cdot3^{18}\)

\(B=2^{28}\cdot3^{18}\cdot\left(5\cdot1\cdot3-7\cdot2\cdot1\right)\)

\(B=2^{28}\cdot3^{18}\cdot\left(15-14\right)\)

\(B=2^{28}\cdot3^{18}\)

Ta có: \(A:B\)

\(=\left(-2^{31}\cdot3^{18}\right):\left(2^{28}\cdot3^{18}\right)\)

\(=\left(-2^{31}:2^{28}\right)\cdot\left(3^{18}:3^{18}\right)\)

\(=-2^3\cdot1\)

\(=-8\)