a)\(162:y+216:y=6\)

⇔\(\left(162+216\right):y=6\)

⇔\(378:y=6\)

⇔\(y=63\)

b)\(602:y+123.2=253\)

⇔\(602:y+246=253\)

⇔\(602:y=7\)

⇔\(y=86\)

c)\(8\left(15720-y\right)=51784\)

⇔\(125760-8y=51784\)

⇔\(8y=73976\)

⇔\(y=9247\)

Ai nhanh mk tick cho

tui 

áp dụng quy tính tổng số là tính đcj

1+2+3+...+y=253

y×(y+1)/2=253

y×(y+1)=253×2=506

Vế trái là 2 số tự nhiên liên tiếp nên y=22

Vậy y=22

cảm ơn các bạn

`B=(x-x/(x+1))-(1-x/(x+1))`

`đkxđ:x ne +-1`

`=((x^2+x-x)/(x+1))-(x+1-x)/(x+1)`

`=x^2/(x+1)-1/(x+1)`

`=(x^2-1)/(x+1)`

`=((x-1)(x+1))/(x+1)`

`=x-1`

`2)(x-1)^2-25`

`=(x-1)^2-5^2`

`=(x-1-5)(x-1+5)`

`=(x-6)(x+4)`

Bài 1: 

Ta có: \(B=\left(x-\dfrac{x}{x+1}\right)-\left(1-\dfrac{x}{x+1}\right)\)

\(=\left(\dfrac{x\left(x+1\right)-x}{x+1}\right)-\left(\dfrac{x+1-x}{x+1}\right)\)

\(=\dfrac{x^2+x-x-\left(x+1-x\right)}{x+1}\)

\(=\dfrac{x^2-1}{x+1}=x-1\)

Bài 2: 

Ta có: \(\left(x-1\right)^2-25\)

\(=\left(x-1-5\right)\left(x-1+5\right)\)

\(=\left(x-6\right)\left(x+4\right)\)

602:x+123x2=253

602:x+246=253

602:x=253-246

602:x=7

x=602:7

x=86

a) \(2\times x+3\times x=\frac{5}{2}\)

=> \(\left(2+3\right)\times x=\frac{5}{2}\)

=> \(5\times x=\frac{5}{2}\)

=> \(x=\frac{5}{2}:5=\frac{5}{2}\times\frac{1}{5}=\frac{1}{2}\)

b) \(145+x\times12-432=253\)

=> \(145+x\times12=253+432\)

=> \(145+x\times12=685\)

=> \(x\times12=685-145\)

=> \(x\times12=540\Rightarrow x=45\)

Câu a) 2 x X + 3 x X = 5/2

          ( 2+3 ) x X       = 5/2

             5      x X       = 5/2

                        X       =5/2 : 5

                        X       = 1/2

Câu b) 145 + X x 12 - 432 = 253

            145 + X x 12          = 253 + 432

            145 + X x 12          = 685

             X x 12                   = 685 - 145

             X x 12                   = 540

             X                          = 540 : 12

            X                           = 45

1) \(x^2y+x\left(2y-1\right)=7\)

\(\Leftrightarrow x^2y+2xy-x=7\)

\(\Leftrightarrow xy\left(x+2\right)-x-2=7-2\)

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

\(\Leftrightarrow\left(xy-1\right)\left(x+2\right)=5\)

\(\Rightarrow\)xy - 1 và x + 2 là ước của 5 là \(\pm1;\pm5\)

đến đây tự lm đc

2 ) \(B=\frac{255}{1}+\frac{254}{2}+\frac{253}{3}+....+\frac{3}{253}+\frac{2}{254}+\frac{1}{255}\)

\(=\left(\frac{254}{2}+1\right)+\left(\frac{253}{3}+1\right)+....+\left(\frac{2}{254}+1\right)+\left(\frac{1}{255}+1\right)+1\)

\(=\frac{256}{2}+\frac{256}{3}+....+\frac{256}{255}+\frac{256}{256}\)

\(=256\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+....+\frac{1}{255}+\frac{1}{256}\right)=256A\)

\(\Rightarrow\frac{B}{A}=256=16^2\) Là số CP (đpcm)

ừ, z câu 2 đâu?

\(a,250:\left(10-x\right)=25\\ \Rightarrow10-x=250:25\\ \Rightarrow10-x=10\\ \Rightarrow x=10-10=0\\ b,3x-2018:2=23\\ \Rightarrow3x-1009=23\\ \Rightarrow3x=23+1009\\ \Rightarrow3x=1032\\ \Rightarrow x=1032:3=344\\ c,\left(9x-21\right):3=2\\ \Rightarrow9x-21=2\times3\\ \Rightarrow9x-21=6\\ \Rightarrow9x=21+6\\ \Rightarrow9x=27\\ \Rightarrow x=27:9=3\)

\(d,53\left(9-x\right)=53\\ \Rightarrow9-x=53:53\\ \Rightarrow9-x=1\\ \Rightarrow x=9-1=8\)