Theo đề bài ta có : 1/4 + 1/3 : 2x = -5

                           1/3 : 2x = -5 - 1/4= -21/4

                             2x = 1/3 : (-21/4) = -4/63

                             x = -4/63 : 2 = -2/63

\(\frac{1}{4}+\frac{1}{3}\div2X=-5\)

ko biết ko hiểu

1/3:2x = -5 - 1/4

1/3 : 2x = 9/2

        2x = 1/3 : 9/2

        2x = 2/27

          x = 2 : 2/27

          x = 27 

 Vậy x = 27 

Chúc bạn học tốt VẬY NHÉ !!!!

a)  x + 12 = (-5) - x

=> chuyển vế : x + x = -12 - 5

=> 2x = -17

=> x = \(-\frac{17}{2}\)

b)  2 . (x - 1) + 3 . (x-2) = x - 4

=> 2x - 2 + 3x - 6 = x - 4

=> chuyển vế: 2x +3x - x = 2 + 6 - 4

=> 4x = 4   => x = 1

c)  4 . (2x +7) - 3 . (3x-2) = 24

=> 8x + 28 - 9x +6 = 24

=> - x = -28 - 6 + 24

=> x = 10

d)  3 . ( x-2) + 2x = 10  (Ý bạn c là x đúng không?)

=> 3x - 6 + 2x = 10

=> 5x = 6 + 10

=> 5x = 16   => x = \(\frac{16}{5}\) 

                  Đúng thì k mik nha. Thanks!

\(a,x+12=\left(-5\right)-x\)

\(x+x=12-5\)

\(2x=7\Leftrightarrow x=\frac{7}{2}\)

\(b,2\left(x-1\right)+3\left(x-2\right)=x-4\)

\(2x-2+3x-6=x-4\)

\(2x+3x-x=-4+2+6\)

\(4x=4\Leftrightarrow x=1\)

\(c,4\left(2x+7\right)-3\left(3x-2\right)=24\)

\(4x+28-9x+6=24\)

\(4x-9x=24-28-6\)

\(-5x=-10\Leftrightarrow x=2\)

\(d,3\left(x-2\right)+2x=10\)

\(3x-6+2x=10\)

\(3x+2x=10+6\)

\(5x=16\Leftrightarrow x=\frac{16}{5}\)

a,\(x+12=\left(-5\right)-x\)

\(=>x+x=-5-12=-17\)

\(=>x=\frac{-17}{2}\)

b,\(2.\left(x-1\right)+3.\left(x-2\right)=x-4\)

\(=>2x-2+3x-6=x-4\)

\(=>2x+3x-x=-4+2+6\)

\(=>4x=4\)

\(=>x=1\)

c,

Bài 1 không có cơ sở để tính biểu thức.

Bài 2:

a. 

$(6x+1)^2+(6x-1)^2-2(6x+1)(6x-1)$

$=[(6x+1)-(6x-1)]^2=2^2=4$

b.

$3(2^2+1)(2^4+1)(2^8+1)(2^{16}+1)$

$=(2^2-1)(2^2+1)(2^4+1)(2^8+1)(2^{16}+1)$

$=(2^4-1)(2^4+1)(2^8+1)(2^{16}+1)$

$=(2^8-1)(2^8+1)(2^{16}+1)$
$=(2^{16}-1)(2^{16}+1)=2^{32}-1$

c.

$2C=(5^2-1)(5^2+1)(5^4+1)(5^8+1)(5^{16}+1)$

$=(5^4-1)(5^4+1)(5^8+1)(5^{16}+1)$

$=(5^8-1)(5^8+1)(5^{16}+1)$
$=(5^{16}-1)(5^{16}+1)=5^{32}-1$

$\Rightarrow C=\frac{5^{32}-1}{2}$

Tìm x:

1. 3x (2x + 3) - (2x + 5).(3x - 2) = 8

\(\Leftrightarrow6x^2+9x-6x^2+4x-15x+10=0 \)

\(\Leftrightarrow-2x+10=0\Leftrightarrow x=5\)

Vậy x = 5

2. 4x (x -1) - 3(x² - 5) -x² = (x - 3) - (x + 4)

\(\Leftrightarrow4x^2-4x-3x^2+15-x^2=x-3-x-4\)

\(\Leftrightarrow-4x+15=-7\)

\(\Leftrightarrow-4x=-22\Leftrightarrow x=\frac{11}{2}\)

Vậy x = \(\frac{11}{2}\)

3. 2 (3x -1) (2x +5) - 6 (2x - 1) (x + 2) = -6

\(\Leftrightarrow2\left(6x^2+15x-2x-5\right)-6\left(2x^2+4x-x-2\right)=-6\)

\(\Leftrightarrow12x^2+30x-4x-10-12x^2-24x+6x+12=-6\)

\(\Leftrightarrow8x=-8\Leftrightarrow x=-1\)

Vậy x = -1

4. 3 ( 2x - 1) (3x - 1) - (2x - 3) (9x - 1) - 3 = -3

\(\Leftrightarrow3\left(6x^2-2x-3x+1\right)-18x^2+2x+27x-3-3=-3\)

\(\Leftrightarrow18x^2-6x-9x+3-18x^2+2x+27x-6=-3\)

\(\Leftrightarrow14x=0\Leftrightarrow x=0\)

Vậy x = 0

5. (3x - 1) (2x + 7) - ( x + 1) (6x - 5) = (x + 2) - (x - 5)

\(\Leftrightarrow6x^2+21x-2x-7-6x^2+5x-6x+5=7\)

\(\Leftrightarrow18x=9\Leftrightarrow x=\frac{1}{2}\)

Vậy x = \(\frac{1}{2}\)

6. 3xy (x + y) - (x + y) (x² + y² + 2xy) + y³ = 27

\(\Leftrightarrow3x^2y+3xy^2-\left(x+y\right)^3+y^3=27\)

\(\Leftrightarrow3x^2y+3xy^2-x^3-y^3-3x^2y-3xy^2+y^3=27\)

\(\Leftrightarrow-x^3=27\)

\(\Leftrightarrow x=-3\)

Vậy x = -3

7. 3x (8x - 4) - 6x (4x - 3) = 30

\(\Leftrightarrow24x^2-12x-24x^2+12x=30\)

\(\Leftrightarrow0=30\) ( vô lý)

Vậy pt vô nghiệm

8. 3x (5 - 2x) + 2x (3x - 5) = 20

\(\Leftrightarrow15x-6x^2+6x^2-10x=20\)

\(\Leftrightarrow5x=20\Leftrightarrow x=4\)

Vậy x = 4

Tìm GTNN của biểu thức :

\(x^2+2x+4\)

Đặt A = \(x^2+2x+4\)

\(\Leftrightarrow A=\left(x^2+2.x.1+1\right)+3\)

\(\Leftrightarrow A=\left(x+1\right)^2+3\)

Ta luôn có : \(\left(x+1\right)^2\ge0\forall x\)

Suy ra : \(\left(x+1\right)^2+3\ge3\forall x\)

Hay A\(\ge3\) với mọi x

Dấu "=" xảy ra khi \(x+1=0\Rightarrow x=-1\)

Nên : \(A_{min}=3khix=-1\)

1e) Để \(\frac{2x-1}{x-3}\) nguyên thì \(2x-1⋮x-3\)

\(\Leftrightarrow2x-6+5⋮x-3\)

\(\Leftrightarrow2\left(x-3\right)+5⋮x-3\)

Do \(2\left(x-3\right)⋮x-3\) \(\Rightarrow5⋮x-3\)

\(\Rightarrow x-3\in\left\{-5;-1;1;5\right\}\)

\(\Leftrightarrow x\in\left\{-2;2;4;8\right\}\)

Vậy:...................

a) \(\left(x+1\right)\left(x+2\right)\left(x+4\right)\left(x+5\right)-4=\left(x^2+6x+5\right)\left(x^2+6x+8\right)-4\)

Đặt \(t=x^2+6x+5\)

\(PT=t\left(t+3\right)-4=t^2+3t-4=\left(t-1\right)\left(t+4\right)\)

Thay t: \(PT=\left(x^2+6x+5-1\right)\left(x^2+6x+5+4\right)=\left(x^2+6x+4\right)\left(x^2+6x+9\right)=\left(x^2+6x+4\right)\left(x+3\right)^2\)

b)  Đặt \(t=\left(2x+1\right)^2\)

\(PT=t^2-3t+2=\left(t^2-3t+\dfrac{9}{4}\right)-\dfrac{1}{4}=\left(t+\dfrac{3}{2}\right)^2-\dfrac{1}{4}=\left(t+1\right)\left(t+2\right)\)

Thay t:

\(PT=\left[\left(2x+1\right)^2+1\right]\left[\left(2x+1\right)^2+2\right]=\left[4x^2+4x+2\right]\left[4x^2+4x+3\right]=2\left[2x^2+2x+1\right]\left[4x^2+4x+3\right]\)