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6 tháng 2 2018

a, (3x-1)(x2+2)=(3x-1)(7x-10)

<=>(3x-1)(x2+2)-(3x-1)(7x-10)=0

<=>(3x-1)(x2+2-7x+10)=0

<=>(3x-1)(x2-7x+12)=0

<=>(3x-1)(x2-3x-4x+12)=0

<=>(3x-1)(x-3)(x-4)=0

<=>\(\left[{}\begin{matrix}3x-1=0\\x-3=0\\x-4=0\end{matrix}\right.\)<=>\(\left[{}\begin{matrix}x=\dfrac{1}{3}\\x=3\\x=4\end{matrix}\right.\)

Vậy ft có tập nghiệm S=\(\left\{\dfrac{1}{3},3,4\right\}\)

b,\(\dfrac{t+3}{t-2}+\dfrac{t-2}{t+3}=\dfrac{5t+15}{t^2+t-6}\) (ĐKXĐ:t\(\ne2;t\ne-3\))

<=>\(\dfrac{\left(t+3\right)^2+\left(t-2\right)^2}{\left(t-2\right)\left(t+3\right)}\)=\(\dfrac{5t+15}{t^2-2t+3t-6}\)

<=>\(\dfrac{t^2+6t+9+t^2-4t+4}{\left(t-2\right)\left(t+3\right)}\)=\(\dfrac{5t+15}{\left(t-2\right)\left(t+3\right)}\)

=>2t2+2t+13=5t+15

<=>2t2+2t-5t+13-15=0

<=>2t2-3t-2=0

<=>2t2-4t+t-2=0

<=>(t-2)(2t+1)=0

<=>\(\left[{}\begin{matrix}t-2=0\\2t+1=0\end{matrix}\right.< =>\left[{}\begin{matrix}t=2\left(loại\right)\\t=\dfrac{-1}{2}\left(tmđkxđ\right)\end{matrix}\right.\)

Vậy ft có nghiệm duy nhất x=\(\dfrac{-1}{2}\)

6 tháng 2 2018

Giải:

a) \(\left(3x-1\right)\left(x^2+2\right)=\left(3x-1\right)\left(7x-10\right)\)

Chia cả hai vế cho 3x-1, ta được:

\(x^2+2=7x-10\)

\(\Leftrightarrow x^2-7x+10+2=0\)

\(\Leftrightarrow x^2-7x+12=0\)

\(\Leftrightarrow x^2-4x-3x+12=0\)

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

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

\(\Leftrightarrow\left[{}\begin{matrix}x-3=0\\x-4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=4\end{matrix}\right.\)

Vậy ...

b) \(\dfrac{t+3}{t-2}+\dfrac{t-2}{t+3}=\dfrac{5t+15}{t^2+t-6}\) (1)

ĐKXĐ: \(t\ne2;t\ne-3\)

\(\left(1\right)\Leftrightarrow\dfrac{\left(t+3\right)\left(t+3\right)}{\left(t-2\right)\left(t+3\right)}+\dfrac{\left(t-2\right)\left(t-2\right)}{\left(t-2\right)\left(t+3\right)}=\dfrac{5t+15}{\left(t-2\right)\left(t+3\right)}\)

\(\Rightarrow\left(t+3\right)^2+\left(t-2\right)^2=5t+15\)

\(\Leftrightarrow t^2+6t+9+t^2-4t+4=5t+15\)

\(\Leftrightarrow2t^2+2t+13=5t+15\)

\(\Leftrightarrow2t^2+2t+13-5t-15=0\)

\(\Leftrightarrow2t^2-3t-2=0\)

\(\Leftrightarrow2t^2-4t+t-2=0\)

\(\Leftrightarrow2t\left(t-2\right)+\left(t-2\right)=0\)

\(\Leftrightarrow\left(2t+1\right)\left(t-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}2t+1=0\\t-2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}t=-\dfrac{1}{2}\left(tm\right)\\t=2\left(ktm\right)\end{matrix}\right.\)

Vậy ...

9 tháng 3 2018

a, \(\dfrac{t+3}{t-2}+\dfrac{t-2}{t+3}=\dfrac{5t+15}{t^2+t-6}\) ĐKXĐ: t\(\ne\)2,t\(\ne\)-3

\(\Leftrightarrow\dfrac{t+3}{t-2}+\dfrac{t-2}{t+3}=\dfrac{5t+15}{\left(t+3\right)\left(t-2\right)}\)

\(\Rightarrow\left(t+3\right)\left(t+3\right)+\left(t-2\right)\left(t-2\right)=5t+15\)

\(\Leftrightarrow t^2+6t+9+t^2-4t+4-5t-15=0\)

\(\Leftrightarrow-3t-2=0\)

\(\Leftrightarrow-3t=2\)

\(\Leftrightarrow t=\dfrac{-2}{3}\) (tđk)

\(\Rightarrow S=\left\{\dfrac{-2}{3}\right\}\)

b, \(\left(2x+3\right)\left(\dfrac{3x+8}{2-7x}+1\right)=\left(x-5\right)\left(\dfrac{3x+8}{2-7x}+1\right)\)ĐKXĐ: x\(\ne\)\(\dfrac{2}{7}\)

\(\Leftrightarrow\) \(\left(2x+3\right)\left(\dfrac{3x+8}{2-7x}+1\right)-\left(x-5\right)\left(\dfrac{3x+8}{2-7x}+1\right)=0\)

\(\Rightarrow\left(\dfrac{3x+8}{2-7x}+1\right)\left(2x+3-x+5\right)=0\)

\(\Leftrightarrow\) \(\Rightarrow\left(\dfrac{3x+8}{2-7x}+1\right)\left(x+8\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{3x+8}{2-7x}+1=0\\x+8=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}3x+8+2-7x=0\\x=-8\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}-4x+10=0\\x=-8\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{2}\\x=-8\end{matrix}\right.\)

\(\Rightarrow S=\left\{\dfrac{5}{2};-8\right\}\)

9 tháng 3 2018

ĐKXĐ: x khác 2 và x khác -3

\(\dfrac{t+3}{t-2}+\dfrac{t-2}{t+3}=\dfrac{5t+15}{t^2+t-6}\)

\(\Leftrightarrow\dfrac{\left(t+3\right)\left(t+3\right)}{\left(t+3\right)\left(t-2\right)}+\dfrac{\left(t-2\right)\left(t-2\right)}{\left(t+3\right)\left(t-2\right)}=\dfrac{5t+15}{t^2+t-6}\)

\(\Rightarrow t^2+6t+9+t^2-4=5t+15\)

\(\Leftrightarrow2t^2+t-10=0\)

\(\Leftrightarrow2t^2-4t+5t-10=0\)

\(\Leftrightarrow2t\left(t-2\right)+5\left(t-2\right)=0\)

\(\Leftrightarrow\left(2t+5\right)\left(t-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}t=2\left(loại\right)\\t=\dfrac{-5}{2}\end{matrix}\right.\)

Vậy..................

5 tháng 3 2018

\(\dfrac{t+3}{t-2}+\dfrac{t-2}{t+3}=\dfrac{5t+15}{t^2+t-6}\)(đkxđ: t khác 2, t khác -3)

<=>\(\dfrac{t+3}{t-2}+\dfrac{t-2}{t+3}=\dfrac{5t+15}{\left(t-2\right)\left(t+3\right)}\)

<=>\(\dfrac{\left(t+3\right)^2}{\left(t-2\right)\left(t+3\right)}+\dfrac{\left(t-2\right)^2}{\left(t+3\right)\left(t-2\right)}=\dfrac{5t+15}{\left(t-2\right)\left(t+3\right)}\)

=>t^2+6t+9+t^2-4t+4=5t+15

<=>2t^2-2t-5t=15-9-4=0

<=>2t^2-7t=0

<=> t(2t-7)=0

<=>t=0

2t-7=0<=>t=-7/2

vậy.....

4 tháng 3 2018

a,

\(\dfrac{1+x+3-3x-3+x}{1-x}=0\\ \dfrac{1-x}{1-x}=0\\ =>1-x=0\\ =>x=1\\ \)

20 tháng 3 2018

b =>x-3 =10x -15

=>x-10x=-15+3

=>-9x=-12

=>x=4/3

Câu 1:

a: ĐKXĐ: x<>1/3; x<>-1/3

b: \(M=\dfrac{-9x^2-3x+6x^2-2x}{\left(3x+1\right)\left(3x-1\right)}\cdot\dfrac{\left(3x-1\right)^2}{2\left(3x^2+5\right)}\)

\(=\dfrac{-3x+1}{3x+1}\)

c: x=1/3 thì loại bởi nó không thỏa ĐKXĐ

4 tháng 3 2018

\(A=\dfrac{1}{x^2+3x+2}+\dfrac{1}{x^2+5x+6}+\dfrac{1}{x^2+7x+12}+\dfrac{1}{x^2+9x+20}\)

\(\Leftrightarrow\dfrac{1}{x^2+2x+x+2}+\dfrac{1}{x^2+2x+3x+6}+\dfrac{1}{x^2+3x+4x+12}+\dfrac{1}{x^2+4x+5x+20}\)

\(\Leftrightarrow\dfrac{1}{\left(x+1\right)\left(x+2\right)}+\dfrac{1}{\left(x+2\right)\left(x+3\right)}+\dfrac{1}{\left(x+3\right)\left(x+4\right)}+\dfrac{1}{\left(x+4\right)\left(x+5\right)}\left(1\right)\)

a, ĐKXĐ của pt : ​

\(\left\{{}\begin{matrix}x+1\ne0\\x+2\ne0\\x+3\ne0\\x+4\ne0\end{matrix}\right.\)\(x+5\ne0\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ne-1\\x\ne-2\\x\ne-3\\x\ne-4\end{matrix}\right.\)\(x\ne-5\)

b, pt(1) \(=\dfrac{1}{x+1}-\dfrac{1}{x+2}+\dfrac{1}{x+2}-\dfrac{1}{x+3}+\dfrac{1}{x+3}-\dfrac{1}{x+4}+\dfrac{1}{x+4}-\dfrac{1}{x+5}\)

\(=\dfrac{1}{x+1}-\dfrac{1}{x+5}\)

\(=\dfrac{x+5-x-1}{\left(x+1\right)\left(x+5\right)}\)

\(=\dfrac{4}{x^2+6x+5}\)

c, Thay x = 3 vào bt trên ,có :

\(\dfrac{4}{3^2+6.3+5}=\dfrac{4}{32}=\dfrac{1}{8}\)

Vậy tại ..............

d, Để \(A=\dfrac{1}{3}\)

\(\Leftrightarrow\dfrac{4}{x^2+6x+5}=\dfrac{1}{3}\)

\(\Leftrightarrow x^2+6x+5=12\)

\(\Leftrightarrow x^2+6x-7=0\)

\(\Leftrightarrow x^2-7x+x-7=0\)

\(\Leftrightarrow\left(x-7\right)\left(x+1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-7=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=7\left(t/m\right)\\x=-1\left(kot/m\right)\end{matrix}\right.\)

Vậy x = 7 thì A = 1/3

4 tháng 3 2018

Mình giải được rồi, cảm ơn bạn. Nhưng câu d đáp án sai rồi nhé. Do chỗ bạn tách 6x ra -7x + x ấy, đúng ra là 7x - x nhé! Đáp án có 2 nghiệm là 1 và -7 nha bạn.

27 tháng 11 2017

a) \(A = \frac{2x^2 - 16x+43}{x^2-8x+22}\) = \(\frac{2(x^2-8x+22)-1}{x^2-8x+22}\) = \(2 - \frac{1}{x^2-8x+22}\)

Ta có : \(x^2-8x+22 \) = \(x^2-8x+16+6 = ( x-4)^2 +6 \)

\((x-4)^2 \ge 0 \) với \( \forall x\in R\) Nên \(( x-4)^2 +6 \ge 6 \)

\(\Rightarrow \) \(x^2-8x+22 \) \( \ge 6\)\(\Rightarrow \) \(\frac{1}{x^2-8x+22} \) \(\le \frac{1}{6}\) \(\Rightarrow \) - \(\frac{1}{x^2-8x+22} \) \(\ge - \frac{1}{6}\)

\(\Rightarrow \) A = \(2 - \frac{1}{x^2-8x+22}\) \( \ge 2-\frac{1}{6}\) = \(\frac{11}{6}\) Dấu "=" xảy ra khi và chỉ khi x=4

Vậy GTNN của A = \(\frac{11}{6}\) khi và chỉ khi x=4

10 tháng 12 2018

1.

a) \(x\left(x+4\right)+x+4=0\)

\(\Leftrightarrow\left(x+1\right)\left(x+4\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+4=0\\x+1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-4\\x=-1\end{matrix}\right.\)

b) \(x\left(x-3\right)+2x-6=0\)

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

\(\Leftrightarrow\left[{}\begin{matrix}x+2=0\\x-3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-2\\x=3\end{matrix}\right.\)

10 tháng 12 2018

Bài 1:

a, \(x\left(x+4\right)+x+4=0\)

\(\Leftrightarrow x\left(x+4\right)+\left(x+4\right)=0\)

\(\Leftrightarrow\left(x+4\right)\left(x+1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+4=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-4\\x=-1\end{matrix}\right.\)

Vậy \(x=-4\) hoặc \(x=-1\)

b, \(x\left(x-3\right)+2x-6=0\)

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

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

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

Vậy \(x=3\) hoặc \(x=-2\)

10 tháng 6 2017

Bài 1:

\(\left(\dfrac{x}{x^2-49}-\dfrac{x-7}{x^2+7x}\right):\dfrac{2x-7}{x^2+7x}+\dfrac{x}{7-x}\)

\(=\left(\dfrac{x}{\left(x-7\right)\left(x+7\right)}-\dfrac{x-7}{x\cdot\left(x+7\right)}\right)\cdot\dfrac{x^2+7x}{2x-7}+\dfrac{x}{-\left(x-7\right)}\)

\(=\dfrac{x^2-\left(x-7\right)^2}{x\cdot\left(x-7\right)\left(x+7\right)}\cdot\dfrac{x\cdot\left(x+7\right)}{2x-7}-\dfrac{x}{x-7}\)

\(=\dfrac{\left(x-\left(x-7\right)\right)\cdot\left(x+x-7\right)}{x-7}\cdot\dfrac{1}{2x-7}-\dfrac{x}{x-7}\)

\(=\dfrac{\left(x-x+7\right)\cdot\left(2x-7\right)}{x-7}\cdot\dfrac{1}{2x-7}-\dfrac{x}{x-7}\)

\(=\dfrac{7}{x-7}-\dfrac{x}{x-7}\)

\(=\dfrac{7-x}{x-7}\)

\(=\dfrac{-\left(x-7\right)}{x-7}\)

\(=-1\)

10 tháng 6 2017

A = \(\left(\dfrac{x}{x^2-49}-\dfrac{x-7}{x^2+7x}\right):\dfrac{2x-7}{x^2+7x}+\dfrac{x}{7-x}\)

A = \(\left(\dfrac{x}{\left(x+7\right)\left(x-7\right)}-\dfrac{x-7}{x\left(x+7\right)}\right):\dfrac{2x-7}{x\left(x+7\right)}+\dfrac{x}{7-x}\)

A = \(\left(\dfrac{x^2-\left(x-7\right)^2}{\left(x+7\right)\left(x-7\right)x}\right):\dfrac{2x-7}{x\left(x+7\right)}-\dfrac{x}{x-7}\)

A = \(\left(\dfrac{x^2-\left(x^2-14x+49\right)}{\left(x+7\right)\left(x-7\right)x}\right):\dfrac{\left(2x-7\right)\left(x-7\right)-\left(x^3+7x^2\right)}{\left(x+7\right)\left(x-7\right)x}\)

A = \(\dfrac{14x-49}{\left(x+7\right)\left(x-7\right)x}:\dfrac{-x^3-5x^2-21x+49}{\left(x+7\right)\left(x-7\right)x}\)

A = \(\dfrac{14x-49}{\left(x+7\right)\left(x-7\right)x}.\dfrac{\left(x+7\right)\left(x-7\right)x}{-x^3-5x^2-21x+49}\)

A = \(\dfrac{14x-49}{-x^3-5x^2-21x+49}\)