+ \(72:\left(x-15\right)=8\)

\(x-15=9\)

\(x=24\)

+ \(\dfrac{3}{90}-3x=3\)

\(3\left(\dfrac{1}{90}-x\right)=3\)

\(\dfrac{1}{90}-x=1\)

\(x=\dfrac{1}{90}-1=\dfrac{-89}{90}\)

b1 A=10000 B=23386

b2 a,x=5 

b,x=4 x=2 

có lẽ bn nên tự lm thì hơn

a: \(x^2-10x=-25\)

\(\Leftrightarrow x-5=0\)

hay x=5

b: \(x^2-6x+8=0\)

\(\Leftrightarrow\left(x-2\right)\left(x-4\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=4\end{matrix}\right.\)

21) 125x³ -1

=125x³-1³

=(5x-1)(25x²+5x+1)

22) 4x⁴ - 9x²

=x²(4x²-9)

=x²(4x²-3²)

=x²(2x-3)(2x+3)

23) 64x² - 25y⁴

=(8x)²-(5y²)²

=(8x-5y²)(8x+5y²)

24) 4( a + b )² - 9( a - b )²

=2²(a+b)²-3²(a-b)²

=[2(a+b)]²-[3(a-b)]²

=[2(a+b)-3(a-b)][2(a+b)+3(a-b)]

=(2a+2b-3a+3b)(2a+2b+3a-3b)

=(5a-b)(5b-a)

25) 8( x + 1 )³ - 27( x - 1 )³

=2³(x+1)³-3³(x-1)³

=[2(x+1)]³-[3(x-1)]³

={[2(x+1)]-[3(x-1)}{[2(x+1)]²+[2(x+1)]*[3(x-1)]+[3(x-1)]²}

={2x+2-3x+3}{4x²+8x+4+6x²-6+9x²-18x+9}

=(5-x)(19x²-10x+7)

a) 9x-32=31

9x=32+31

9x=63
x=63:9
x=7

b)23(450-5x)=2346

450-5x=2346:23

450-5x=102

-5x=102-450

-5x=-348

x=-348:(-5)

x=69,6

c) x:8+ 64:8=20

x:8 +8=20

x:8=20-8
x:8=12
x=12.8
x=96

d) 7.2^x=112

2^x=112:7

2^x=16

mà 2⁴=16

=> x=4

e) 5.4^x=320

4^x=320:5

4^x=64

mà 4³ =64

=> x=3

g) [5.(70-x)+2³ .3² ] :4 =28

(350-x + 8.9) = 28.4

350-x+72=112

-x=112-350-72

-x=-310

=> x=310

a) 9x - 32 = 31

     9x       = 31 + 32

     9x       = 63

       x       = 63 : 9

      x         = 7

bạn ơi bạn cố gắng suy nghĩ và làm tiếp cho mình nhé

\(\left(3x+4\right)^3=\left(9x-8\right)\left(3x^2-8\right)\)

\(27x^3+108x^2+144x+64=27x^3-72x-24x^2+64\)

\(27x^3-27x^3+108x^2+24x^2+144x+72x=64-64=0\)

\(132x^2+216x=0\)

\(x\left(132x+216\right)=0\)

\(\Rightarrow x=\hept{\begin{cases}0\\\frac{216}{132}=\frac{18}{11}\end{cases}}\)

Bài làm :

\(a,23+x:2=37\)

\(x:2=14\)

\(x=14\times2\)

\(x=28\)

\(b,x-320:32=4\times16\)

\(x-10=64\)

\(x=64+10\)

\(x=74\)

\(c,3x-2018:2=23\)

\(3x-1009=23\)

\(3x=23+1009\)

\(3x=1032\)

\(x=344\)

\(d,\left(9x-21\right):3=2\)

\(9x-21=6\)

\(9x=6+21\)

\(9x=27\)

\(x=3\)

\(e,15:x+120:12=15\)

\(15:x+10=15\)

\(15:x=15-10\)

\(15:x=5\)

\(x=3\)

Học tốt nhé

(9x-2³):5=2

⇒(9x-8):5=2

⇒9x-8=2.5=10

⇒9x=10+8=18

⇒x=18:9

⇒x=2

x = 2

Bài 1

S₂ = 21 + 23 + 25 + ... + 1001

Số số hạng của S₂:

(1001 - 21) : 2 + 1 = 491

⇒ S₂  = (1001 + 21) . 491 : 2 = 250901

--------

S₄  = 15 + 25 + 35 + ... + 115

Số số hạng của S₄:

(115 - 15) : 10 + 1 = 11

⇒ S₄ = (115 + 15) . 11 : 2 = 715

Bài 2

a) 2x - 138 = 2³.3²

2x - 138 = 8.9

2x - 138 = 72

2x = 72 + 138

2x = 210

x = 210 : 2

x = 105

b) 5.(x + 35) = 515

x + 35 = 515 : 5

x + 35 = 103

x = 103 - 35

x = 78

c) 814 - (x - 305) = 712

x - 305 = 814 - 712

x - 305 = 102

x = 102 + 305

x = 407

d) 20 - [7.(x - 3) + 4] = 2

7(x - 3) + 4 = 20 - 2

7(x - 3) + 4 = 18

7(x - 3) = 18 - 4

7(x - 3) = 14

x - 3 = 14 : 7

x - 3 = 2

x = 2 + 3

x = 5

e) 9ˣ⁻¹ = 9

x - 1 = 1

x = 1 + 1

x = 2

2:

a: \(2x-138=2^3\cdot3^2\)

=>\(2x-138=8\cdot9=72\)

=>2x=138+72=210

=>x=105

b: \(5\cdot\left(x+35\right)=515\)

=>x+35=103

=>x=103-35=68

c: \(814-\left(x-305\right)=712\)

=>x-305=814-712=102

=>x=102+305=407

d: \(20-\left[7\left(x-3\right)+4\right]=2\)

=>7(x-3)+4=18

=>7(x-3)=14

=>x-3=2

=>x=5

e: \(9^{x-1}=9\)

=>x-1=1

=>x=2

f: \(5^{x-2}-3^2=2^4-\left(2^8\cdot2^2-2^{10}\cdot2^2\right)\)

=>\(5^{x-2}-9=16-1024+4096\)

=>\(5^{x-2}=3097\)

=>\(x-2=log_53097\)

=>\(x=2+log_53097\)