- x × 3 = 30

X = 30 : 3

X = 10

- 2 × x = 10

X = 10 : 2

X = 5

- x : 4 = 5

X = 5 × 4

X = 20

a) 467 + x = 877 – 162

467 + x = 715

x = 715 – 467

x = 248

b) x – 214 = 61 + 345

x – 214 = 406

x = 406 + 214

x = 620

c) x : 5 = 10 × 2

x : 5 = 20

x = 20 × 5

x = 100

d) x × 4 = 30 – 10

x × 4 = 20

x = 20 : 4

x = 5

Lời giải:

$x\vdots -2$ nên $x$ là số chẵn.

Mà $-10\leq x\leq 2$ nên $x\in\left\{-10; -8; -6; -4; -2; 0;2\right\}$

------------

$-30\vdots x$ mà $x$ nguyên nên $x$ là ước của $-30$

$\Rightarrow x\in\left\{\pm 1; \pm 2; \pm 3; \pm 5; \pm 6; \pm 10; \pm 15; \pm 30\right\}$

a) x+32=5

x=5-32

x=-27

b)x-4=-7

x=-7+4

x=-3

c) 10-(x+12)=5-(22-30)

10-x-12=5-22+30

-2-x=13

x=-2-13

=-15

#H

\(\frac{1}{30}:x:\frac{10}{15}=4\times\frac{1}{5}\)

\(\Rightarrow\frac{1}{30}:x:\frac{2}{3}=\frac{4}{5}\)

\(\Rightarrow\frac{1}{30}:x=\frac{2}{3}\times\frac{4}{5}\)

\(\Rightarrow\frac{1}{30}:x=\frac{8}{15}\)

\(\Rightarrow x=\frac{1}{30}::\frac{8}{15}\)

\(\Rightarrow x=\frac{1}{16}\)

\(\frac{1}{30}:x:\frac{10}{15}=4\cdot\frac{1}{5}\)

\(\frac{1}{30}:x:\frac{2}{3}=\frac{4}{5}\)

\(\frac{1}{30}:x=\frac{4}{5}\cdot\frac{2}{3}\)

\(\frac{1}{30}:x=\frac{8}{15}\)

\(x=\frac{1}{30}:\frac{8}{15}\)

\(x=\frac{1}{16}\)

Vậy X=\(\frac{1}{16}\)

<=> \(\frac{1.2.3....31}{4.6.8....64}=2^n\Rightarrow\frac{1.2.3....30.31}{2\left(2.3.4.5...31\right).32}=2^n\Leftrightarrow\frac{1}{2.32}=2^n\Leftrightarrow\frac{1}{2^6}=2^n\)

=> 2^6.2^n = 1 

=> 2^ (n + 6 ) = 2^0

=> n+ 6  = 0 

=> n = - 6 

\(\frac{1}{4}.\frac{2}{6}.\frac{3}{8}....\frac{31}{64}=\frac{1.2.3....31}{4.6.8....64}=\frac{1.2.3....31}{2.3.2.4....2.32}=\frac{1.2.3....31}{2^{30}.\left(3.4....32\right)}=\frac{2}{2^{30}.32}=\frac{1}{2^{34}}=2^{-34}=2^n=>n=-34\)

2^n × 2³¹ = \(\dfrac{ }{ }\)2/4×4/6×6/8×...×62/64

2^n×2³¹=1/32=2^-5

2^n=2^-5 ÷ 2³¹=2^-36

=>n=-36

\(C=\left(x^4-2x.5x^2+25x^2\right)+\left(x^2-2.5x+25\right)+5.\)

\(C=\left(x^2-5x\right)^2+\left(x-5\right)^2+5\ge5\)

giá trị nhỏ nhất của C là 5 dấu  xảy ra khi 

\(\left(x^2-5x\right)^2+\left(x-5\right)^2=0\Leftrightarrow x=5\)

Bài 1:

a. $(-20)+x=-30$

$x-20=-30$

$x=-30+20=-(30-20)=-10$

b.

$(-10)-x=-20$

$x=(-10)-(-20)=-10+20=20-10=10$

c. Đề sai. Bạn xem lại.

d.

$x+(-3)=-7$

$x=-7-(-3)=-7+3=-(7-3)=-4$

e.

$x-(-5)=-9$

$x=(-9)+(-5)=-14$

f.

$x(-11)=12$

$x=\frac{12}{-11}=\frac{-12}{11}$

h.

$2x-10=20$

$2x=20+10=30$

$x=30:2=15$

l.

$4x-8=-8$
$4x=-8+8=0$

$x=0:4=0$

k.

$-12-(-2)x=-8$

$(-2)x=-12-(-8)=-12+8=-(12-8)=-4$

$x=(-4):(-2)=2$

Bài 2:

a. $-20-(10-x)=-3$

$10-x=-20-(-3)=-20+3=-(20-3)=-17$

$x=10-(-17)=10+17=27$

b.

$14+(14-x)=-2$
$14-x=-2-14=-16$

$x=14-(-16)=14+16=30$

c.

$-15-(x-3)=-7$

$x-3=-15-(-7)=-15+7=-8$

x=-8+3=-5$

d.

$(x+4)+(-20)=-8$

$x+4=-8-(-20)=-8+20=12$
$x=12-4=8$

e.

$-2x-2=-4$

$-2x=-4+2=-2$

$x=(-2):(-2)=1$

f.

$-2x+4=-4$

$-2x=-4-4=-8$

$x=(-8):(-2)=4$

l.

$-12-(-2)x=-2-4=-6$

$(-2)x=-12-(-6)=-12+6=-6$

$x=(-6):(-2)=3$