a)-7x+7=21                                          

-7x=21-7

-7x=16

x=16:-7

x=-16/7

\(a,-7x+7=21\)

\(\Rightarrow-7x=21-7=14\)

\(\Rightarrow x=-2\)

\(b,9x+11=20x+66\)

\(\Rightarrow9x-20x=66-11=55\)

\(\Rightarrow-11x=55\)

\(\Rightarrow x=-5\)

\(c,3^3.x+4^2=5^2.x-2.\left(2017\right)^0\)

\(27x+16=25x-2\)

\(\Rightarrow16+2=25x-27x=-2x\)

\(\Rightarrow-2x=18\)

\(\Rightarrow x=-9\)

\(d,\left(2+3+...+20\right)x=2100\)

\(\Rightarrow\frac{\left(20+2\right)\left[\left(20-2\right):1+1\right]}{2}x=2100\)

\(11.19.x=2100\)

\(\Rightarrow x\simeq10\)

\(e,5\left(\left|x\right|-14\right)=10\)

\(\Rightarrow\left|x\right|-14=10:5=2\)

\(\Rightarrow\left|x\right|=16\)

\(\Rightarrow x=\orbr{\begin{cases}16\\-16\end{cases}}\)

Lời giải:

a.

$\frac{2}{3}+\frac{1}{3}:3\times x=20\text{%}$
$\frac{2}{3}+\frac{1}{9}\times x=\frac{1}{5}$

$\frac{1}{9}\times x=\frac{1}{5}-\frac{2}{3}=\frac{-7}{15}$

$x=\frac{-7}{15}: \frac{1}{9}=\frac{-21}{5}$
b.

$\frac{3-x}{5-x}=\frac{6}{11}$
$\Rightarrow 6(5-x)=11(3-x)$

$\Rightarrow 30-6x=33-11x$

$\Rightarrow 5x=3$

$\Rightarrow x=\frac{3}{5}$

a: \(\Leftrightarrow x=\dfrac{33}{20}:\dfrac{11}{8}=\dfrac{33}{20}\cdot\dfrac{8}{11}=3\cdot\dfrac{2}{5}=\dfrac{6}{5}\)

b: \(\Leftrightarrow x=5:\dfrac{4}{7}=\dfrac{35}{4}\)

\(x:33=\dfrac{9}{66}\)
\(x=\dfrac{9}{66}\times33\)
\(x=\dfrac{9}{2}\)
\(\dfrac{4}{5}\times x=\dfrac{10}{11}:\dfrac{3}{4}\)
\(\dfrac{4}{5}\times x=\dfrac{40}{33}\)
\(x=\dfrac{40}{33}:\dfrac{4}{5}\)
\(x=\dfrac{50}{33}\)
#Đạt Đang Bận Thở

bài 2 tìm x

a,106- ( x+ 7) =9

x+7 = 106 - 9

x+7 = 107

x= 107 - 7

x=100

b, 2 x ( x+ 4) + 5 =65

2 x (x+4) = 65 - 5

2 x (x+4) = 60

x+4 = 60:2

x+4= 30

x= 30 - 4

x=26

c, (16x x -32) x 45=0

16 x X - 32 = 0: 45

16 x X - 32 =0

16 x X = 0 + 32

16 x X = 32

X= 32:16

X=2

d, x+4 x x = 100 : 5

X + 4 x X = 20

(1+4) x X = 20

5 x X  = 20

X= 20:5

X=4

Bài 1:

a, 24 x 66 - 24 + 36 x 24

= 24 x (66-1+36)

= 24 x 101

= 24 x 100 + 24

= 2400+24

=2424

b, 29 x 173 - 29 x 72 - 29

= 29 x (173 - 72 -1)

= 29 x 100

= 2900

c, 1+5+10+15+...+55+60

= (5+60) x 6 + 1 (có 6 cặp)

= 65 x 6 + 1

= 390 +1 =391

d, D= 1 x 2 + 2 x 3 + 3 x 4 +...+18 x 19 + 19 x 20

3D= 1 x 2 x 3+ 2 x 3 x (4-1) + 3 x 4 x (5-2) +...+ 18 x 19 x (20 - 17) + 19 x 20 x (21-18)

3D= 1 x 2 x 3 - 1 x 2 x 3 + 2 x 3 x 4 - 2 x 3 x 4 +.... + 19 x 20 x 21 - 18 x 19 x 20

3D= 19 x 20 x 21 =7980

=> D= 7980:3=2660

a) Ta có: \(\left(2x-8\right)\left(2x+10\right)\ge0\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-8\ge0\\2x+10\le0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x\ge4\\x\le-5\end{matrix}\right.\)

b) Ta có: \(\left(\left|x\right|+5\right)\left(x-3\right)< 0\)

nên x-3<0

hay x<3

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.

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

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

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

Bạn chia từng bài ra được chứ?

a) \(\dfrac{4}{7}\times x=\dfrac{5}{9}+\dfrac{1}{5}=\dfrac{34}{45}\)

\(x=\dfrac{34}{45}:\dfrac{4}{7}=\dfrac{119}{90}\)

b) \(\dfrac{11}{15}:x=\dfrac{2}{3}-\dfrac{9}{15}=\dfrac{1}{15}\)

\(x=\dfrac{11}{15}:\dfrac{1}{15}=11\)

a) 4/7 x X - 1/5 = 5/9   

     4/7 x X         = 5/9 + 1/5

     4/7 x X         =  34/45

             X          = 34/45 : 4/7

             X          =  119/90

 b)9/15 + 11/15 : X = 2/3

               11/15 : X = 2/3 - 9/15

               11/15 : X =  1/15

                           X = 11/15 : 1/5 

                           X = 11