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Câu hỏi của Nguyễn Đăng Khôi - Toán lớp 8 - Học toán với OnlineMath

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1)(x+1)(x+2)(x+3)=x³+6x²+11x+6

2)a)3x(x-5)-(x-1)(2+3x)=30

<=>3x²-15x-3x²+x+2=30

<=>-14x+2=30

<=>-14x=30-2

<=>-14x=28

<=>x=-2

b)(x+2)(x+3)-(x-2)(x+5)=0

<=>x²+5x+6-x²-3x+10=0

<=>2x+16=0

<=>2x=-16

<=>x=-8

c)(3x+2)(2x+9)-(x+2)(6x+1)=9

<=>6x²+31x+18-6x²-13x-2=9

<=>18x+16=9

<=>18x=9-16

<=>18x=-7

<=>x=-7/18

\(a,\Rightarrow4x^2-20x-4x^2+3x+4x-3=5\\ \Rightarrow-13x=8\Rightarrow x=-\dfrac{8}{13}\\ b,\Rightarrow3x^2-10x+8-3x^2+27x=-3\\ \Rightarrow17x=-11\Rightarrow x=-\dfrac{11}{17}\\ c,\Rightarrow\left(x+3\right)\left(2-x\right)=0\Rightarrow\left[{}\begin{matrix}x=-3\\x=2\end{matrix}\right.\\ d,\Rightarrow2x\left(4x^2-25\right)=0\\ \Rightarrow2x\left(2x-5\right)\left(2x+5\right)=0\Rightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{2}{5}\\x=-\dfrac{2}{5}\end{matrix}\right.\\ e,Sửa:\left(4x-3\right)^2-3x\left(3-4x\right)=0\\ \Rightarrow\left(4x-3\right)^2+3x\left(4x-3\right)=0\\ \Rightarrow\left(4x-3\right)\left(7x-3\right)=0\Rightarrow\left[{}\begin{matrix}x=\dfrac{3}{4}\\x=\dfrac{3}{7}\end{matrix}\right.\)

a.

4x(x-5) - (x-1)(4x-3)-5=0

 4x^2-20x-4x^2+3x+4x+3=0

(4x^2-4x^2)+(-20x+3x+4x)+3=0

 13x+3 = 0

13x=-3

x=-3/13

b,

(3x-4)(x-2)-3x(x-9)+3=0

3x^2-6x-4x+8 - 3x^2+27x+3=0

(3x^2-3x^2)+(-6x-4x+27x)+(8+3)=0

17x+11=0

17x=-11

x=-11/17

c, 2(x+3)-x^2-3x=0

2(x+3) - x(x+3)=0

(x+3)(2-x)=0

TH1: x+3 = 0; x=-3

TH2: 2-x=0;x=2

Ta có:

\(\left(3x-5\right)\left(5-3x\right)+9\left(x+1\right)^2=30\)

\(\Leftrightarrow9\left(x^2+2x+1\right)-\left(3x-5\right)\left(3x-5\right)=30\)

\(\Leftrightarrow9x^2+18x+9-\left(9x^2-30x+25\right)=30\)

\(\Leftrightarrow48x-16=30\)

\(\Leftrightarrow48x=46\Leftrightarrow x=\dfrac{23}{24}\)

cái dell gì zợ????????????

(3x - 5)(5 - 3x) + 9(x + 1)^2 = 30

=> 15x - 9x^2 - 25 + 15x + 9(x^2 + 2x + 1) = 30

=> 30x - 9x^2 - 25 + 9x^2 + 18x + 9 = 30

=> 38x - 16 = 30

=> 38x = 46

=> x = 23/19

\(\left(3x-5\right)\left(5-3x\right)+9\left(x+1\right)^2=30.\)

\(15x-9x^2-25+15x+9\left(x^2+2x+1\right)=30\)

\(15x-9x^2-25+15x+9x^2+18x+9=30\)

\(48x-16=30\)

\(48x=30+16=46\)

\(x=\frac{46}{48}=\frac{23}{24}\)

  \(\left(x+4\right)^2-\left(x+1\right)\left(x-1\right)=16\)

\(x^2+8x+16-\left(x^2-1\right)=16\)

\(x^2+8x+16-x^2+1=16\)

\(8x+17=16\)

\(8x=16-17=-1\)

\(x=-\frac{1}{8}\)