`@` `\text {Ans}`

`\downarrow`

`a)`

`5(x + 35) = 515`

`=> x + 35 = 515 \div 5`

`=> x+ 35 = 103`

`=> x = 103 - 35`

`=> x = 68`

Vậy, `x = 68`

`b)`

`12x - 33 = 3^2 * 3^3`

`=> 12x - 33 = 3^5`

`=> 12x = 3^5 + 33`

`=> 12x = 276`

`=> x = 276 \div 12`

`=> x = 23`

Vậy, `x = 23`

`c)`

`6x - 5 = 19`

`=> 6x = 19 + 5`

`=> 6x = 24`

`=> x = 24 \div 6`

`=> x = 4`

Vậy, `x = 4`

`d)`

`4(x - 12) + 9 = 17`

`=> 4(x - 12) = 17 - 9`

`=> 4(x - 12) = 8`

`=> x - 12 = 8 \div 4`

`=> x - 12 = 2`

`=> x = 14`

Vậy, `x = 14`

`e)`

123 - 5(x + 4) = 38`

`=> 5(x + 4)= 123 - 38`

`=> 5(x + 4) =85`

`=> x + 4 = 85 \div 5`

`=> x + 4 = 17`

`=> x = 13`

Vậy, `x = 13`

`f)`

`(3x - 2^4) * 7^3 = 2 * 7^4`

`=> 3x - 2^4 = 2 * 7^4 \div 7^3`

`=> 3x - 2^4 = 2* 7`

`=> 3x - 2^4 = 14`

`=> 3x = 14 + 2^4`

`=> 3x = 30`

`=> x = 30 \div 3`

`=> x = 10`

Vậy, `x = 10.`

2/ 5x ( 12x + 7 ) - ( 3x + 1 ) ( 20x - 5 ) = -100

\(\Leftrightarrow\) 60x² + 35x - 60x² + 15x - 20x + 5 = -100

\(\Leftrightarrow\) 30x = -100 - 5

\(\Leftrightarrow\) x = - 3,5

4/ ( x + 5 ) ² + ( x + 4 ) ( x - 4 ) = 0

\(\Leftrightarrow\) x² + 10x + 25 + x² - 4 = 0

\(\Leftrightarrow\) 2x² + 10x + 21 = 0

---> Phương trình vô nghiệm

Sửa đề bài : 4/ ( x + 5 ) ² - ( x + 4 ) ( x - 4 ) = 0

\(\Leftrightarrow\) x² + 10x + 25 - x² + 4 = 0

\(\Leftrightarrow\) 10x = - 29

\(\Leftrightarrow\) x = \(-\dfrac{29}{10}\)

Vậy phương trình có nghiệm.......

ý 4/ bấm máy tính không ra nghiệm --> đề bài sai

d. \(\sqrt{9x^2+12x+4}=4\)

<=> \(\sqrt{\left(3x+2\right)^2}=4\)

<=> \(|3x+2|=4\)

<=> \(\left[{}\begin{matrix}3x+2=4\\3x+2=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}3x=2\\3x=-6\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{2}{3}\\x=-2\end{matrix}\right.\)

c: Ta có: \(\dfrac{5\sqrt{x}-2}{8\sqrt{x}+2.5}=\dfrac{2}{7}\)

\(\Leftrightarrow35\sqrt{x}-14=16\sqrt{x}+5\)

\(\Leftrightarrow x=1\)

\(1,\)

\(A=-\frac{7}{12}+\frac{12}{18}+\frac{5}{4}\)

\(=-\frac{7}{12}+\frac{2}{3}+\frac{5}{4}\)

\(=-\frac{7}{12}+\frac{8}{12}+\frac{15}{12}\)

\(=\frac{-7+8+15}{12}\)

\(=\frac{4}{3}\)

\(1,\)

\(B=\frac{1}{4}-\frac{8}{7}:8-3:\frac{3}{4}.\left(-2\right)^2\)

\(=\frac{1}{4}-\frac{8}{7}.\frac{1}{8}-3.\frac{4}{3}.4\)

\(=\frac{1}{4}-\frac{1}{7}-16\)

\(=\frac{7-4-448}{28}\)

\(=-\frac{445}{28}\)

Mình đang bận, bạn cần gấp thế à? Trả lời trong tin nhắn nhé!!!

2.B=1/4-(8/7:8)-(3:3/8).(-2)^2=1/4-(8/7.1/8)-(3/1.4/3).(-2)^2=1/4-1/7-4.(-2)^2=1/4-1/7-16= 7/28-4/28-448/28= -445/28

Bài 1: 

a) \(-5\left(x^2-3x+1\right)+x\left(1+5x\right)=x-2\)

\(\Rightarrow-5x^2+15x-5+x+5x^2=x-2\)

\(\Rightarrow16x-5=x-2\)

\(\Rightarrow16x-x=5-2\)

\(\Rightarrow15x=3\)

\(\Rightarrow x=\dfrac{15}{3}=5\)

b) \(12x^2-4x\left(3x+5\right)=10x-17\)

\(\Rightarrow12x^2-12x^2-20x=10x-17\)

\(\Rightarrow-20x=10x-17\)

\(\Rightarrow-20x-10x=-17\)

\(\Rightarrow-30x=-17\)

\(\Rightarrow x=\dfrac{-30}{-17}=\dfrac{30}{17}\)

c) \(-4x\left(x-5\right)+7x\left(x-4\right)-3x^2=12\)

\(\Rightarrow-4x^2+20x+7x^2-28x-3x^2=12\)

\(\Rightarrow-8x=12\)

\(\Rightarrow x=\dfrac{12}{-8}=-\dfrac{4}{3}\)

Bài 2: 

a) \(\left(x+5\right)\left(x-7\right)-7x\left(x-3\right)\)

\(=x^2-7x+5x-35-7x^2+21x\)

\(=-6x^2+19x-35\)

b) \(x\left(x^2-x-2\right)-\left(x-5\right)\left(x+1\right)\)

\(=x^3-x^2-2x-x^2+x-5x-5\)

\(=x^3-2x^2-6x-5\)

c) \(\left(x-5\right)\left(x-7\right)-\left(x+4\right)\left(x-3\right)\)

\(=x^2-7x-5x+35-x^2-3x+4x-12\)

\(=11x+23\)

d) \(\left(x-1\right)\left(x-2\right)-\left(x+5\right)\left(x+2\right)\)

\(=x^2-2x-x+2-x^2+2x+5x+10\)

\(=4x+12\)

Yêu cầu?