\(\dfrac{x-3}{13}+\dfrac{x-3}{14}=\dfrac{x-3}{15}+\dfrac{x-3}{16}\)

\(\Leftrightarrow x-3=0\)

hay x=3

ai giúp mình với khó quá

=>(x-3)(1/13+1/14-1/15-1/16)=0

=>x-3=0

=>x=3

`(x-3)/13+(x-3)/14=(x-3)/15+(x-3)/16`

`=>(x-3).(1/13+1/14-1/15-1/16)=0`

`=>x-3=0` 

`=>x=3`
 

\(\dfrac{x-3}{13}+\dfrac{x-3}{14}=\dfrac{x-3}{15}+\dfrac{x-3}{16}\)

\(\Leftrightarrow\dfrac{x-3}{13}+\dfrac{x-3}{14}-\dfrac{x-3}{15}-\dfrac{x-3}{16}=0\)

\(\Leftrightarrow\left(x-3\right).\left(\dfrac{1}{13}+\dfrac{1}{14}-\dfrac{1}{15}-\dfrac{1}{16}\right)=0\)

\(\Leftrightarrow x-3=0\)( Vì \(\dfrac{1}{13}+\dfrac{1}{14}-\dfrac{1}{15}-\dfrac{1}{16}>0\))

\(\Leftrightarrow x-3=0\Rightarrow x=3\)

\(\dfrac{x-3}{13}+\dfrac{x-3}{14}=\dfrac{x-3}{15}+\dfrac{x-3}{16}\)

\(\Leftrightarrow\dfrac{1680.\left(x-3\right)+1560.\left(x-3\right)-1456.\left(x-3\right)-1365.\left(x-3\right)}{21840}=0\)

\(\Leftrightarrow\left(x-3\right).\left(1680+1560-1456-1365\right)=0\)

\(\Leftrightarrow\left(x-3\right).419=0\)

\(\Leftrightarrow419x=1257\)

\(\Leftrightarrow x=3\)

Lời giải:

\(\frac{x-3}{13}+\frac{x-3}{14}=\frac{x-3}{15}+\frac{x-3}{16}\)

\((x-3)\left(\frac{1}{13}+\frac{1}{14}\right)=(x-3)\left(\frac{1}{15}+\frac{1}{16}\right)\)

\((x-3)\left[\left(\frac{1}{13}+\frac{1}{14}\right)-\left(\frac{1}{15}+\frac{1}{16}\right)\right]=0\)

Ta thấy:

\(\frac{1}{13}>\frac{1}{15}; \frac{1}{14}>\frac{1}{16}\Rightarrow \frac{1}{13}+\frac{1}{14}> \frac{1}{15}+\frac{1}{16}\)

Do đó biểu thức trong ngoặc vuông lớn hơn $0$ hay khác $0$

$\Rightarrow x-3=0$

$\Leftrightarrow x=3$

Bạn ơi bạn làm đc bao nhiêu thì làm phụ mình nhé 

bài1

a, 

5 - 7 + 3 +(-8)

= -2 + 3 + ( - 8)

=     1    + (-8)= -7

a; - (-5) - (+7) + (+3) + (-8)

  = 5 - 7 + 3  - 8

= (5 + 3 - 8) - 7

= (8 - 8) - 7

= 0 - 7

= - 7

1. -x+20 = -(-15)-8+13

=> -x=15-8+13-20

=> -x=0

=> x=0

2. -(-10)+x=-13+(-9)+(-6)

=> 10+x=-13-9-6

=> x = -13-9-6-10

=> x = -38

3. 8-(-12)+10=-(-14)-x

=> 8+12+10=14-x

=> x = 14-8-12-10

=> x = -16

4. -(+12)+(-x)-(-3)=5-(-7)

=> -12-x+3=5+7

=> -x=5+7+12-3

=> -x=21

=> x=-21

5. 14-x+(-10)=-(-9)+(+15)

=> 14-x-10=9+15

=> -x=9+15-14+10

=> -x=20

=> x=-20

6. 12-(-17)+(-3)=-5+x

=> 12+17-3+5=x

=> x=31

7. x-(-19)-(+32)=14-(+16)

=> x+19-32=14-16

=> x=14-16+32-19

=> x=11

8. x-|-15|-|7|=-(-9)+|-5|

=> x-15-7=9+5

=> x=9+5+7+15

=> x=36

9. 15-x+17=13-(-21)

=> 15-x+17=13+21

=> -x=13+21-15-17

=> -x=2

=> x=-2

10. -|-5|-(-x)+4=3-(-25)

=> -5+x+4=3+25

=> x=3+25-4+5

=> x=29

Bạn viết như này ai hiểu

Viết lại đề lại sách nháp đi

\(\Rightarrow\frac{\left(\frac{518}{19}-\frac{342}{13}\right).\left(\frac{253}{236}-\frac{3}{318}\right)}{\left(\frac{3}{4}+x\right)\frac{27}{33}}\)=\(\frac{\frac{1}{3}.\frac{3}{36}+\frac{1}{3}.\frac{3}{14.17}}{\frac{1}{2}.\frac{2}{13.15}+\frac{1}{2}.\frac{2}{14.16}}\)

\(\frac{\frac{236}{2247}.\frac{247}{236}}{\left(\frac{3}{4}+x\right)\frac{27}{33}}\)=\(\frac{\frac{1}{3}.\left(\frac{1}{13}-\frac{1}{16}+\frac{1}{14}-\frac{1}{17}\right)}{\frac{1}{2}\left(\frac{1}{13}+\frac{1}{14}-\frac{1}{16}-\frac{1}{17}\right)}\)

\(\frac{1}{\left(\frac{3}{4}+x\right)\frac{27}{33}}\)=\(\frac{\frac{1}{3}}{\frac{1}{2}}\)

đến đây tự làm nhé cứ ra 13/12 là được