Bài 1: 

Ta có:

\(y-x=25\Rightarrow y=25+x\)

Mà \(7x=4y\Rightarrow7x=4\cdot\left(25+x\right)\)

\(7x=100+4x\)

\(\Rightarrow7x-4x=100\)

\(3x=100\)

\(x=\frac{100}{3}\)

bài 1 :

Ta có: 7x=4y ⇔ x/4=y/7

áp dụng tính chất dãy tỉ số bằng nhau ta có 

x/4=y/7=(y-x)/(7-4)=100/3

⇒x= 4 x 100/3=400/3 ; y = 7 x 100/3=700/3

bài 2 

ta có x/5 = y/6 ⇔ x/20=y/24

         y/8 = z/7 ⇔ y/24=z/21

⇒x/20=y/24=z/21

ADTCDTSBN(bài 1 có)

x/20=y/24=z/21=(x+y)/(20+24)=69/48=23/16

⇒x= 20 x 23/16 = 115/4

   y= 24x 23/16=138/2

   z=21x23/16=483/16

bài 3

x:y:z=3:8:5  ⇔ x/3=y/8=z/5

ADTCDTSBN

x/3=y/8=z/5=(3x+y-4z)/(9+8-10)=14/7=2

⇒x = 2x3 = 6 ; y= 2x8=`16; z=2x5=10

a) (-5) mũ 5

b) (-2) mũ 3 x (-3) mũ 3

giống Vũ Duy nha

Từ : anime xxx

a) \(\left(-5\right).\left(-5\right).\left(-5\right).\left(-5\right).\left(-5\right)=\left(-5\right)^5\)

b)\(\left(-2\right).\left(-2\right).\left(-2\right).\left(-3\right).\left(-3\right).\left(-3\right)=\left(-2\right)^3.\left(-3\right)^3\)

a. \(\frac{7}{8}< \frac{x}{35}< \frac{15}{7}\)

\(\Rightarrow\frac{245}{280}< \frac{8x}{280}< \frac{600}{280}\)

\(\Rightarrow245< 8x< 600\)

\(\Rightarrow30< x< 75\)

\(\Rightarrow x\in\left\{31;32;33;...;72;73;74\right\}\)

b. \(\frac{21}{3}< \frac{x}{7}\le\frac{24}{2}\)

\(\Rightarrow\frac{294}{42}< \frac{6x}{42}\le\frac{504}{42}\)

\(\Rightarrow294< 6x\le504\)

\(\Rightarrow49< x\le84\)

\(\Rightarrow x\in\left\{50;51;52;...;82;83;84\right\}\)

cảm ơn bn nha

Giải

Có: \(\frac{7}{8}< \frac{x}{35}< \frac{15}{7}\)

=>\(\frac{245}{280}< \frac{x}{280}< \frac{525}{280}\)

=>\(\frac{245}{280}< 1< ....< \frac{525}{280}\)

=>\(x\in\left\{8;9;...;14\right\}\)

b, \(\frac{21}{3}< \frac{x}{7}\le\frac{24}{2}\)

=>\(7< \frac{x}{7}\le12\)

=>\(\frac{49}{7}< \frac{x}{7}\le\frac{12}{7}\)

=>\(\frac{x}{7}=\left\{\frac{12}{7};\frac{14}{7};\frac{21}{7};\frac{28}{7};\frac{35}{7};\frac{42}{7}\right\}\)

=>\(x\in\left\{12;14;21;28;35;42\right\}\)

Chúc bạn học tốt

đây bạn

a) -x - 84=-16-213

   -x-84=-229

    -84+229=x

        145 =x

b) /x+2/= 316

suy ra x+2=316 hoac x+2=-316

  * x+2 = 316

       x = 314

* x+2 =-316

    x   = -318

vay x=314 hoac x=-318

c) /x+7/=15

suy ra x+7=15 hoac x+7=-15

   x+7=15

     x  = 8

   x+7= -15

     x = -22

vay x= 8 hoac x=-22

d) 19-4=/x-1/

   15=/x-1/

suy ra x-1=15 hoac x-1=-15

x-1=15

   x = 16

x-1=-15

  x= -14

vay x=16 hoac x=-14

\(-\left(x+84\right)+213=-16\)

\(=>-x-84+213=-16\)

\(=>-x=-16+84-213=-145\)

\(=>x=145\)

\(\left|x+2\right|=341+\left(-25\right)\)

\(=>\left|x+2\right|=341-25=316\)

\(=>\orbr{\begin{cases}x+2=316\\x+2=-316\end{cases}}\)

\(=>\orbr{\begin{cases}x=314\\x=-318\end{cases}}\)

\(\left|x+7\right|=\left|-15\right|\)

\(=>\left|x+7\right|=15\)

\(=>\orbr{\begin{cases}x=15-7\\x=-15-7\end{cases}}\)

\(=>\orbr{\begin{cases}x=8\\x=-22\end{cases}}\)

\(19-\left|x-1\right|=4\)

\(=>\left|x-1\right|=19-4=15\)

\(=>\orbr{\begin{cases}x-1=15\\x-1=-15\end{cases}}\)

\(=>\orbr{\begin{cases}x=16\\x=-14\end{cases}}\)

a, 5/2 + 3/4 : x = -1/2

=> x = -1/4

b, 1/2 . x + 3/5 . x = -2/3

=> x = -20/33

c, 4/7 . x - x = -9/14

=> x = 3/2

128 - 3.(x+4) = 25-2

128 - 3.x - 12 = 23

128 - 12 -3.x = 23

116 - 3.x = 23

3.x = 93

x = 31

các bài còn lại bn dựa vào phần a mak lm nha!
 

128-3(x+4)=25-2

128-3(x+4)=23

       3(x+4)=128-23

       3(x+4)=105

         (x+4)=105:3

           x+4=35

           x    =35-4

           x    =31

128 - 3(x + 4) = 25 - 2

=> 128 - 3(x + 4) = 23

=> 3(x + 4) = 128 - 23

=> 3(x + 4) = 105

=> x + 4 = 105 : 3

=> x + 4 = 35

=> x = 35 - 4

=> x = 31

vậy_

15 - 6x = 3

=> 6x = 15 - 3

=> 6x = 12

=> x = 12 : 6

=> x = 2

vậy_

24 + 5x = 49

=> 5x = 49 - 24

=> 5x = 20

=> x = 20 : 5

=> x = 4

vậy_

219 - 7(x + 1) = 100

=> 7(x + 1) = 219 - 100

=> 7(x + 1) = 119

=> x + 1 = 119 : 7

=> x + 1 = 17

=> x = 17 -1 

=> x = 16

vậy_