a)\(\text{ 4x - 15 = -75 - x}\)

\(4x-15+75+x=0\)

\(5x+60=0\)

\(5x=-60\)

\(x=-14\)

Vậy....

Thêm dấu suy ra trc mỗi dòng nha

Học tốt

b)\(|2x-7|+2=13\)

\(|2x-7|=11\)

\(\Leftrightarrow\hept{\begin{cases}2x-7=11\\2x-7=-11\end{cases}\Leftrightarrow\hept{\begin{cases}2x=18\\2x=4\end{cases}\Leftrightarrow}\hept{\begin{cases}x=9\\x=2\end{cases}}}\)

vậy x=9 hoặc x=2

a) 4x - 15 = -75 - x

4x + x = -75 + 15

5x = -60

x= -60:5

x=-12

b) |2x - 7| + 2 = 13

| 2x - 7 | = 11

th1: 2x-7= 11

2x = 18

x = 9

th2: 2x - 7 = -11

2x = -4

x = -2

c)(2x - 1)^2 = 9

(2x-1)^2= 3^2

2x-1 = 3

2x = 4

x = 2

d)2x (x - 3) = 0

Th1: 2x=0

x= 0

Th2: x- 3 =0

x= 3

Hok tốt!!!

(2x-3/7)(2x^2+18)=0 => 2x-3/7=0 hoặc 2x^2+18=0 => 2x=3/7 hoặc 2x^2=-18(loại vì 2x^2 >= 0)

=>x=3/7 / 2=> x=3/7*1/2=>x=3/14

Vậy : x=3/14

8) \(\left(x+4\right)\left(6x-12\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x+4=0\\6x-12=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-4\\6x=12\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=-4\\x=2\end{cases}}}\)

Vậy \(x\in\left\{-4;2\right\}\)

11) \(\left(\frac{7}{8}-2x\right)\left(3x+\frac{1}{3}\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}\frac{7}{8}-2x=0\\3x+\frac{1}{3}=0\end{cases}\Leftrightarrow\orbr{\begin{cases}2x=\frac{7}{8}-0\\3x=-\frac{1}{3}\end{cases}}\Leftrightarrow\orbr{\begin{cases}2x=\frac{7}{8}\\x=-\frac{1}{9}\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=\frac{7}{16}\\x=-\frac{1}{9}\end{cases}}}\)

Vậy \(x\in\left\{\frac{7}{16};-\frac{1}{9}\right\}\)

12) \(3x-2x^2=0\)

\(\Leftrightarrow x\left(3-2x\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=0\\x=\frac{3}{2}\end{cases}}\)

Vậy \(x\in\left\{0;\frac{3}{2}\right\}\)

13) \(5x+10x^2=0\)

\(\Leftrightarrow5x\left(1+2x\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=0\\x=-\frac{1}{2}\end{cases}}\)

Vậy \(x\in\left\{0;-\frac{1}{2}\right\}\)

8) (x+4)(6x-12)=0

\(\Leftrightarrow\orbr{\begin{cases}x+4=0\\6x-12=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-4\\x=2\end{cases}}}\)

Vậy x={-4;2}

11) \(\left(\frac{7}{8}-2x\right)\left(3x+\frac{1}{3}\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}\frac{7}{8}-2x=0\\3x+\frac{1}{3}=0\end{cases}\Leftrightarrow\orbr{\begin{cases}2x=\frac{7}{8}\\3x=\frac{-1}{3}\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=\frac{7}{16}\\x=\frac{-1}{9}\end{cases}}}\)

\(\frac{5}{7}+y\times\frac{1}{2}=\frac{8}{7}:\frac{3}{2}\)

=> \(\frac{5}{7}+y\times\frac{1}{2}=\frac{8}{7}\times\frac{2}{3}\)

=> \(\frac{5}{7}+y\times\frac{1}{2}=\frac{16}{21}\)

=> \(y\times\frac{1}{2}=\frac{16}{21}-\frac{5}{7}=\frac{1}{21}\)

=> \(y=\frac{1}{21}:\frac{1}{2}=\frac{1}{21}\cdot2=\frac{2}{21}\)

5/7 + Y x 1/2 = 8/7 : 3/2

=> 5/7 + Y x 1/2 = 16/21

=> Y x 1/2 = 16/21 - 5/7

=> Y x 1/2 = 1/21

=> Y = 1/21 : 1/2 

=> Y = 2/21

Hok tốt ^^

Bài 5: 

a: \(8A=8+8^2+...+8^8\)

\(\Leftrightarrow7A=8^8-1\)

hay \(A=\dfrac{8^8-1}{7}\)

b: \(8B=\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\)

\(\Leftrightarrow8B=\left(3^4-1\right)\left(3^4+1\right)\left(3^8+1\right)\)

\(\Leftrightarrow8B=3^{16}-1\)

hay \(B=\dfrac{3^{16}-1}{8}\)

9!-8!-7!.8^2

=362880-40320-5040.64

=322560-322560

=0

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