-x + 20 = - (-15) - (8) + 13 

-x + 20 = 15 - 8 + 13 

-x + 20 = 7 + 13 

- x + 20 = 20

x = 20 - 20 

x = 0

-(-10) + x = -13 + (-9) + (-6) 

10 + x = -13 - 9 - 6 

10 + x = -28 

x = -28 - 10 

x = -38 

8 - (-12) + 10 = -(-14) - x 

8 + 12 + 10 = 14 - x 

30 = 14 - x 

x = 14 - 30 

x = -16

a  tìm số nguyên x biết (x-5).(y-7)=1 
   (x-5).(y-7)=1 = 1.1 = -1.(-1) 
   TH1,
   x-5 = 1, y-7 = 1
   => x = 6, y = 8
   TH2

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

2/3.x + 1/4 = 7/12

2/3.x           = 7/12 - 1/4

2/3.x           = 1/3

x                 = 1/3 : 2/3

x                 = 1/2

Bài làm

\(\frac{2}{3}x+\frac{1}{4}=\frac{7}{12}\)

\(\frac{2}{3}x=\frac{7}{12}-\frac{1}{4}\)

\(\frac{2}{3}x=\frac{7}{12}-\frac{3}{12}\)

\(\frac{2}{3}x=\frac{4}{12}\)

\(\frac{2}{3}x=\frac{1}{3}\)

\(x=\frac{1}{3}:\frac{2}{3}\)

\(x=\frac{1}{3}.\frac{3}{2}\)

\(x=\frac{1}{2}\)

Vậy \(x=\frac{1}{2}\)

2/3 .x + 1/4 = 7/12

2/3 .x         = 7/12 - 1/4

2/3.x          = 1/3

x                = 1/3 : 2/3

x                = 1/2

\(\frac{x+2}{327}+\frac{x+3}{326}+\frac{x+4}{325}+\frac{x+5}{324}+\frac{x+349}{5}=0.\)

\(1+\frac{x+2}{327}+1+\frac{x+3}{326}+1+\frac{x+4}{325}+1+\frac{x+5}{324}-4+\frac{x+349}{5}=0\)

\(\frac{x+329}{327}+\frac{x+329}{326}+\frac{x+329}{325}+\frac{x+329}{324}+\frac{x+329}{5}=0\)

\(\left(x+329\right).\left(\frac{1}{327}+\frac{1}{326}+\frac{1}{325}+\frac{1}{324}+\frac{1}{5}\right)=0\)

\(\Rightarrow x+329=0\)

\(\Rightarrow x=-329\)

Study well 

\(\Rightarrow\frac{x+2}{327}+1+\frac{x+3}{326}+1+\frac{x+4}{325}+1+\frac{x+5}{324}+1+\frac{x+349}{5}-4=0\)

\(\Rightarrow\frac{x+329}{327}+\frac{x+329}{326}+\frac{x+329}{325}+\frac{x+329}{324}+\frac{x+329}{5}=0\)

\(\Rightarrow\left(x+329\right).\left(\frac{1}{327}+\frac{1}{326}+\frac{1}{325}+\frac{1}{324}+\frac{1}{5}\right)=0\)

Mà \(\left(\frac{1}{327}+\frac{1}{326}+\frac{1}{325}+\frac{1}{324}+\frac{1}{5}\right)\ne0\)

Nên \(x+329=0\Rightarrow x=-329\)

Vậy \(x=-329\)

Chúc bạn học tốt !!!

Bài làm

Không viết lại đề nha !

\(=\frac{\left(x+2\right)}{327}+\frac{\left(x+3\right)}{326}+\frac{\left(x+4\right)}{325}+\frac{\left(x+5\right)}{324}+\frac{\left(x+349\right)}{5}=0\)

\(\Leftrightarrow\frac{\left(x+2\right)}{327}+1+\frac{\left(x+3\right)}{326}+1+\frac{\left(x+4\right)}{325}+1+\frac{\left(x+5\right)}{324}+1+\frac{\left(x+349\right)}{5}\)

\(\Leftrightarrow\frac{\left(x+329\right)}{327}+\frac{\left(x+329\right)}{326}+\frac{\left(x+329\right)}{325}+\frac{\left(x+329\right)}{324}+\frac{\left(x+329\right)}{5}-4=0\)

\(\Leftrightarrow\left(x+329\right).\left(\frac{1}{327}+\frac{1}{326}+\frac{1}{325}+\frac{1}{324}+\frac{1}{5}\right)\ne0\)

Nên:x+329=0=>x=-329

Mình làm câu 2 trước nhé:

đkxđ: \(\dfrac{1}{2}< x\le2\)

 Áp dụng BĐT Bunyakovsky, ta có \(VT=\left(1.\sqrt{x}+1.\sqrt{2-x}\right)\)\(\le\sqrt{\left(1^2+1^2\right)\left[\left(\sqrt{x}\right)^2+\left(\sqrt{2-x}\right)^2\right]}\) \(=2\). ĐTXR \(\Leftrightarrow x=2-x\Leftrightarrow x=1\) (nhận). Vậy \(VT\le2\)     (1)

 Mặt khác, ta có \(\left(x-1\right)^2\ge0\) \(\Leftrightarrow x^2-\left(2x-1\right)\ge0\) \(\Leftrightarrow\left(x-\sqrt{2x-1}\right)\left(x+\sqrt{2x-1}\right)\ge0\). Do \(x+\sqrt{2x-1}>0\) nên điều này có nghĩa là \(x\ge\sqrt{2x-1}\) \(\Rightarrow\dfrac{x}{\sqrt{2x-1}}\ge1\) \(\Leftrightarrow\dfrac{2x}{\sqrt{2x-1}}\ge2\) hay \(VP\ge2\)  (2). ĐTXR \(\Leftrightarrow x=1\) (nhận)

 Từ (1) và (2) suy ra \(VT\le2\le VP\), do đó pt đã cho \(\Leftrightarrow VT=VP\) \(\Leftrightarrow x=1\) 

 Vậy pt đã cho có nghiệm duy nhất \(x=1\)

Không=))

y x(5+7)=120

y x 12=120

y=10

X x [5+7] =120

X x 12=120

X =10

y x 5 + 7 x y =120 

y x ( 5 + 7)= 120

y x 12 = 120

y = 10

a) (x - 12). 105 = 0

    x-12= 0 : 105

    x - 12 = 0

   x = 0+ 12

   x = 12

b) (47.(27 - x) = 94

    27-x =94 : 47

    27 - x = 2

    x = 27 - 2

    x = 25

c) 2x + 69 .2 = 69.5

   2x = 69.5 - 69.2

   2x = 69 . (5 - 2)

   2x = 69.3

   2x = 207

   x = 207 : 2

   x = 103,5