Bài 6:

\(21,251+6,058+0,749+1,042\)

\(=\left(21,251+0,749\right)+\left(6,058+1,042\right)\)

\(=22+7,1\)

\(=29,1\)

___________________

\(1,53+5,309+12,47+5,691\)

\(=\left(1,53+12,47\right)+\left(5,309+5,691\right)\)

\(=14+11\)

\(=25\)

5:

a: =>x/17=5/17

=>x=5

b; =>6+x=7/11*33=21

=>x=15

c: \(\dfrac{12+x}{43-x}=\dfrac{2}{3}\)

=>3x+36=86-2x

=>5x=50

=>x=10

d: \(\dfrac{x}{5}< \dfrac{3}{7}\)

=>x<3/7*5

=>x<15/7

f: 15/26+x/16=46/52

=>x/16=23/26-15/26=8/26=4/13

=>x=4/13*16=64/13

a) \(\Rightarrow72-20x-36x+84=30x-240-6x-84\)

\(\Rightarrow80x=480\Rightarrow x=6\)

b) \(\Rightarrow15x+25-8x+12=5x+6x+36+1\)

\(\Rightarrow4x=0\Rightarrow x=0\)

c) \(\Rightarrow10x-16-12x+15=12x-16+11\)

\(\Rightarrow14x=4\Rightarrow x=\dfrac{2}{7}\)

b) Đặt x² + x + 1 = t > 0 (dễ c/m t > 0 rồi ha)

Khi đó, pt tương đương: \(t\left(t+1\right)=12\Leftrightarrow t^2+t-12=0\Leftrightarrow\left[{}\begin{matrix}t=3\\t=-4\left(L\right)\end{matrix}\right.\)

t = 3 suy ra \(x^2+x+1=3\Leftrightarrow x^2+x-2=0\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-2\end{matrix}\right.\)

Vậy...

c) Chị xem lại đề giúp em ạ.

a) 5x - 14 = x - 34

5x - x = -34 + 14

4x = -20

x = -20 : 4

x = -5

b) x - 3 - (3x + 2) = -15

x - 3 - 3x - 2 = -15

x - 3x = -15 + 3 + 2

-2x = -10

x = (-10) : (-2)

x = 5

c) 2(x  - 12) + 19 = x + (-34)

2x - 24 + 19 = x + (-34)

2x - x = -34 + 24 - 19

x = -29

d) 2(x - 33) - 3(x - 43) = 96 - 115

2x - 66 - 3x + 129 = 96 - 115

2x - 3x = 96 - 115 + 66 - 129

-x = -82

x = 82

e) 2x + 3 - 9x = -11

2x - 9x = -11 - 3

-7x = -14

x = (-14) : (-7)

x = 2

f) -(x + 3 - 84) = (x + 70 - 71) - 6

-x - 3 + 84 = x + 70 - 71 - 6

-x - x = 70 - 71 - 6 - 84

-2x = -91

x = (-91) : (-2)

x = 45,5

Bài 22:

a: =>-12x+60+21-7x=5

=>-19x+81=5

=>-19x=-76

=>x=4

b: =>30x+60-6x+30-24x=100

=>90=100(loại)

Noob ơi, bạn phải đưa vào máy tính ý solve cái là ra x luôn, chỉ tội là đợi hơi lâu

a, 4.(18 - 5x) - 12(3x - 7) = 15(2x - 16) - 6(x + 14) 

=> 72 - 20x - 36x + 84 = 30x - 240 - 6x - 84

=> (72 + 84) + (-20x - 36x) = (30x - 6x) + (-240 - 84) 

=> 156 -  56x = 24x - 324 

=>  24x + 56x = 324 + 156 

=> 80x = 480 

=> x = 480 : 80 =  6 

Vậy x = 6 

b, 5(3x + 5) - 4(2x - 3) = 5x + 3(2x + 12) + 1 

=> 15x + 25 - 8x + 12 = 5x + 6x + 36 + 1 

=> (15x - 8x) + (25 + 12) = 11x + 37 

=> 7x + 37 = 11x + 37 

=> 11x - 7x = 0 

=>  x = 0 

\(a,=3x-9-4x+12=-x+3=0\)

\(\Leftrightarrow x=3\)

Vậy ..

\(b,=\left(x+2\right)\left(x+2-x+2\right)=4\left(x+2\right)=0\)

\(\Leftrightarrow x+2=0\)

\(\Leftrightarrow x=-2\)

Vậy ..

\(c,=x^3-3x^2+3x-1=\left(x-1\right)^3=0\)

\(\Leftrightarrow x=1\)

Vậy ..

\(d,\Leftrightarrow x\left(x-2\right)\left(x+2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\\x=-2\end{matrix}\right.\)

Vậy ..

\(e,=\left(2x-3-5\right)\left(2x-3+5\right)=\left(2x-8\right)\left(2x+2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{8}{2}=4\\x=-\dfrac{2}{2}=-1\end{matrix}\right.\)

Vậy ...

a) Ta có: 3(x-3)-4x+12=0

\(\Leftrightarrow3\left(x-3\right)-4\left(x-3\right)=0\)

\(\Leftrightarrow x-3=0\)

hay x=3

Vậy: S={3}

b) Ta có: \(\left(x+2\right)^2-\left(x+2\right)\left(x-2\right)=0\)

\(\Leftrightarrow x^2+4x+4-x^2+4=0\)

\(\Leftrightarrow4x=-8\)

hay x=-2

Vậy: S={-2}

c) Ta có: \(x^3+3x=3x^2+1\)

\(\Leftrightarrow x^3-3x^2+3x-1=0\)

\(\Leftrightarrow x-1=0\)

hay x=1

Vậy: S={1}

d) Ta có: \(\dfrac{2}{3}x\left(x^2-4\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x^2-4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\\x=-2\end{matrix}\right.\)

Vậy: S={0;2;-2}

a) 3.(x-3)-4x+12=0

=> 3x - 9 - 4x + 12 = 0

=> -x + 3 = 0

=> x = 3

b) (x+2)^2-(x+2).(x-2) =0

\(\Rightarrow\left(x+2\right)^2-x^2+4=0\)

\(\Rightarrow x^2+4x+4-x^2+4=0\)

=> 4x + 8 = 0

=> x = -2

c) x^3+3x=3x^2+1

\(\Rightarrow x^3+3x-3x^2-1=0\)

\(\Rightarrow\left(x-1\right)^3=0\)

=> x = 1

d) \(\dfrac{2}{3}x\left(x^2-4\right)=0\)

\(\Rightarrow\dfrac{2}{3}x\left(x-2\right)\left(x+2\right)=0\)

=> x = 0 hoặc x = 2 hoặc x = -2

e) \(\left(2x-3\right)^2-5^2=0\)

\(\Rightarrow\left(2x-8\right)\left(2x+2\right)=0\)

=> x = 4 hoăc x = -1

c) \(\left(34-2x\right)\left(2x-6\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}34-2x=0\\2x-6-0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}2x=34\\2x=6\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=17\\x=3\end{matrix}\right.\)

d) \(\left(2019-x\right)\left(3x-12\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}2019-x=0\\3x-12=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=2019\\3x=12\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=2019\\x=4\end{matrix}\right.\)

e) \(57\left(9x-27\right)=0\)

\(\Rightarrow9x-27=0\)

\(\Rightarrow9\left(x-3\right)=0\)

\(\Rightarrow x-3=0\)

\(\Rightarrow x=3\)

f) \(25+\left(15-x\right)=30\)

\(\Rightarrow25+15-x=30\)

\(\Rightarrow40-x=30\)

\(\Rightarrow x=40-30\)

\(\Rightarrow x=10\)

g) \(43-\left(24-x\right)=20\)

\(\Rightarrow43-24+x=20\)

\(\Rightarrow19+x=20\)

\(\Rightarrow x=20-19\)

\(\Rightarrow x=1\)

h) \(2\left(x-5\right)-17=25\)

\(\Rightarrow2\left(x-5\right)=17+25\)

\(\Rightarrow x-5=21\)

\(\Rightarrow x=21+5\)

\(\Rightarrow x=26\)

i) \(3\left(x+7\right)-15=27\)

\(\Rightarrow3\left(x+7\right)=27+15\)

\(\Rightarrow x+7=14\)

\(\Rightarrow x=14-7\)

\(\Rightarrow x=7\)

j) \(15+4\left(x-2\right)=95\)

\(\Rightarrow4\left(x-2\right)=95-15\)

\(\Rightarrow4\left(x-2\right)=80\)

\(\Rightarrow x-2=20\)

\(\Rightarrow x=20+2\)

\(\Rightarrow x=22\)

k) \(20-\left(x+14\right)=5\)

\(\Rightarrow x+14=20-5\)

\(\Rightarrow x+14=15\)

\(\Rightarrow x=15-14\)

\(\Rightarrow x=1\)

l) \(14+3\left(5-x\right)=27\)

\(\Rightarrow3\left(5-x\right)=27-14\)

\(\Rightarrow3\left(5-x\right)=13\)

\(\Rightarrow5-x=\dfrac{13}{3}\)

\(\Rightarrow x=5-\dfrac{13}{3}\)

\(\Rightarrow x=\dfrac{2}{3}\)

\(1,\Leftrightarrow7x=42\Leftrightarrow x=6\\ 2,\Leftrightarrow36-4x=4\Leftrightarrow4x=32\Leftrightarrow x=8\\ 3,\Leftrightarrow3x=35\Leftrightarrow x=\dfrac{35}{3}\\ 4,\Leftrightarrow x-12=144\Leftrightarrow x=156\\ 5,\Leftrightarrow x-14=16\Leftrightarrow x=30\\ 6,\Leftrightarrow3x-24=\dfrac{148}{73}\Leftrightarrow3x=\dfrac{1900}{73}\Leftrightarrow x=\dfrac{1900}{219}\\ 7,\Leftrightarrow33+x=45\Leftrightarrow x=12\\ 8,Sai.đề\\ 9,\Leftrightarrow\left(x+9\right):2=39\Leftrightarrow x+9=78\Leftrightarrow x=69\\ 11,\Leftrightarrow2\left(x+7\right)=38\Leftrightarrow x+7=19\Leftrightarrow x=12\\ 13,\Leftrightarrow2\left(x-51\right)=66\Leftrightarrow x-51=33\Leftrightarrow x=84\)

\(15,\Leftrightarrow x-19=9\Leftrightarrow x=28\\ 17,\Leftrightarrow\left(x-3\right):2=48\Leftrightarrow x-3=96\Leftrightarrow x=99\\ 19,\Leftrightarrow0x=46\Leftrightarrow x\in\varnothing\\ 8,Sai.đề\\ 14,\Leftrightarrow2x=209\Leftrightarrow x=\dfrac{209}{2}\\ 16,\Leftrightarrow2x+6=157\Leftrightarrow2x=151\Leftrightarrow x=\dfrac{151}{2}\\ 18,\Leftrightarrow5\left(x+4\right)=100\Leftrightarrow x+4=20\Leftrightarrow x=16\\ 20,\Leftrightarrow\left(3x-5\right)^3=27=3^3\Leftrightarrow3x-5=3\Leftrightarrow x=\dfrac{8}{3}\)