a) x-12=-9+15

     x-12=24

     x=24+12

     x=36

Vậy x=36

b)4x -12=400

    4x=412

    x=412:4

   x=103

Vậy x=103

c)2x -35=15

   2x=50

   x=50:2

   x=15

Vậy x=15

d)3x+17=2

   3x=-15

   x=(-15):3

  x=-5

Vậy x=-5

e)\(\frac{-5}{8}=\frac{x}{16}\)

\(\Rightarrow\left(-5\right).16=8.x\)

\(\Rightarrow8x=-80\)

\(\Rightarrow x=-10\)

f)\(\frac{y}{10}=-\frac{4}{8}\)

\(\Rightarrow8y=\left(-4\right).10\)

\(\Rightarrow8y=-40\)

\(\Rightarrow y=-5\)

a) x - 12 = -9 + 15 

=> x - 12 = 6 

=> x = 6 + 12 = 18

b) 4x - 12 = 400 

=> 4x = 400 + 12 = 412

=> x = 412 : 4 = 103

c) 2x - 35 = 15

=> 2x = 15 + 35 = 50

=> x = 50 : 2 = 25

d) 3x + 17 = 2

=> 3x = 2 - 17 

=> 3x = -15

=> x = -15 : 3 = -5

e) \(\frac{-5}{8}=\frac{x}{16}\)

\(=>\frac{-10}{16}=\frac{x}{16}\)

=> x = -10

f) \(\frac{y}{10}=\frac{-4}{8}\)

\(=>\frac{y}{10}=\frac{-1}{2}\)

\(=>\frac{y}{10}=\frac{-5}{10}\)

=> y = -5

a) x - 12 = -9 + 15

x - 12 = 6

x = 12 + 6

x = 18

b) 4x - 12 = 400

4x = 412 

x = 412 : 4

x = 103

c) 2x - 35 = 15

2x = 50

=> x = 25 

d) 3x + 17 = 2

=> 3x = -15

=> x = -5

e) -5/8 = x/16

=> -10/16 = x/16

=> x = -10

y/10 = -4/8

=> y/10 = -40/80

=> y/10 = -5/10

=> y = -5

a) 1 + 1/4 + 1/8 + 1/16

= 16/16 + 4/16 + 2/16 + 1/16

= 23/16

b) 2 - 1/8 - 1/12 - 1/16

= 96/48 - 6/46 - 4/48 - 3/48

= 83/48

c) 4/99 × 18/5 : 12/11 + 3/5

= 8/55 : 12/11 + 3/5

= 2/15 + 3/5

= 2/15 + 9/15

= 11/15

d) (1 - 3/4) × (1 + 1/3) : (1 - 1/3)

= 1/4 × 4/3 : 2/3

= 1/3 : 2/3

= 2

1 + 1/4 + 1/8 + 1/16

= 16 + 4 + 2 + 1 / 16

=23/16

2-1/8-1/12-1/16

= 96 - 6 - 4 - 3 / 48

= 83 / 48

4/99 x 18/5 : 12 /11 + 3/5

= 4/99 x 18/5 x 11/12 + 3/5

= 2/15 + 3/5

= 11/15

(1 - 3/4) x (1+1/3) : (1-1/3) 

= 1/4 x 4/3 : 2/3

= 1/4 x 4/3 x 3/2

= 1/2

Ta có :1.2+2.4+3.6+4.8+5.10/3.4+6.8+9.12+12.16+15.20=[1.2(1+4+9+...+25)]/[3.4(1+4+9+16)]

=(1.2)/(3.4)=2/12=1/6

CHÚC BẠN HỌC TỐT!!

cho tớ nhé!!!!

=2+8+18+32+50/12+48+108+192+300

=110/660

=0.166666667\

giúp mik a.

 a) 8/12 + 9/27 x 4/7

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

= 2/3 + 4/21

= 18/21

= 6/7

b) 8/16 x 36/45 - 4/25

= 1/2 x 4/5 - 4/25

= 2/5 - 4/25

= 6/25

a) 2/3+ 1/3x 4/7

= 2/3 + 4/21

= 14/21+ 4/21

= 18/21 

= 6/7

b) 1/2x 4/5 - 4/25

= 2/5- 4/25

= 10/25 - 4/25

=6/25

dễ mà,tách từng tích ra 1 thừa số chung là:4 thì ra thôi

A = 8 . 12 . 32  + 4 . 27 . 24 + 41 .4 . 16 

A = 96 . 32 + 96 . 27 + 41 . 4 . 16 

A = 96 ( 32 + 27 ) +41 . 4 . 16 

A = 96 . 59  + 41 . 64

A = 32 . 3 . 59 + 41 . 32 . 2 

A = 32 ( 3 + 59 + 41 + 2 )

A  = 32 . 105

A = 3360

a/ \(\dfrac{3-x}{12}=\dfrac{2x+2}{8}\)

\(< =>\dfrac{2\left(3-x\right)}{24}=\dfrac{3\left(2x+2\right)}{24}\)

\(< =>6-2x-6x-6=0\)

\(< =>-8x=0\)

\(< =>x=0\)

Vậy tập nghiệm.....

b/ \(\dfrac{x+3}{x-4}+\dfrac{x-3}{x+4}=\dfrac{2\left(x^2+12\right)}{x^2-16}\)

Tìm ĐKXĐ của pt là: \(x\ne\pm4\)  (làm tắt, bạn làm rõ ra nhé)

\(\dfrac{x+3}{x-4}+\dfrac{x-3}{x+4}=\dfrac{2\left(x^2+12\right)}{x^2-16}\)

\(< =>\dfrac{\left(x+3\right)\left(x+4\right)}{\left(x-4\right)\left(x+4\right)}+\dfrac{\left(x-3\right)\left(x-4\right)}{\left(x-4\right)\left(x+4\right)}=\dfrac{2\left(x^2+12\right)}{\left(x+4\right)\left(x-4\right)}\)

\(< =>x^2+3x+4x+12+x^2-3x-4x+12-2x^2-24=0\)

\(< =>0x=0\)

=> x có vô số nghiệm

Vậy ....

a) `(3-x)/12=(2x+2)/8`

`<=> (3-x)/12 =(x+1)/4`

`<=> 3-x=3(x+1)`

`<=>3-x=3x+3`

`<=> x=0`

Vậy `S={0}`.

b) ĐK: `x \ne \pm 4`

`(x+3)/(x-4)+(x-3)/(x+4)=(2(x^2+12))/(x^2-16)`

`<=> (x+3)(x+4)+(x-3)(x-4)=2(x^2+12)`

`<=> x^2+7x+12+x^2-7x+12=2x^2+24`

`<=> 0x=0`

Vậy PT có nghiệm với mọi x thỏa mãn điều kiện.

\(\dfrac{x+3}{x-4}+\dfrac{x-3}{x+4}=\dfrac{2\left(x^2+12\right)}{x^2-16}\)

⇔\(\dfrac{\left(x+3\right)\left(x+4\right)}{\left(x-4\right)\left(x+4\right)}+\dfrac{\left(x-3\right)\left(x-4\right)}{\left(x-4\right)\left(x+4\right)}=\dfrac{2\left(x^2+12\right)}{\left(x-4\right)\left(x+4\right)}\)

⇔\(\dfrac{x^2+4x+3x+12}{\left(x-4\right)\left(x+4\right)}+\dfrac{x^2-4x-3x+12}{\left(x-4\right)\left(x+4\right)}=\dfrac{2x^2+24}{\left(x-4\right)\left(x+4\right)}\)

⇔\(\dfrac{x^2+7x+12}{\left(x-4\right)\left(x+4\right)}+\dfrac{x^2-7x+12}{\left(x-4\right)\left(x+4\right)}=\dfrac{2x^2+24}{\left(x-4\right)\left(x+4\right)}\)

⇒ \(x^2+7x+12+x^2-7x+12=2x^2+24\)

⇔ \(2x^2+24=2x^2+24\)

⇔ \(2x^2-2x^2=24-24\)

⇔ x=0