PK
1
K
Khách
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HT
23 tháng 5 2016
A=\(\frac{13-x}{x+3}+\frac{6x^2+6}{x^4-8x^2-9}-\frac{3x+6}{\left(x+2\right)\left(x+3\right)}-\frac{2}{x-3}=0\)\(\Leftrightarrow\frac{13-x}{x+3}+\frac{6\left(x^2+1\right)}{\left(x-3\right)\left(x+3\right)\left(x^2+1\right)}-\frac{3\left(x+2\right)}{\left(x+2\right)\left(x+3\right)}-\frac{2}{x-3}=0\) ( với \(x^4-8x^2-9=x^4-9x^2+x^2-9=x^2\left(x^2-9\right)+\left(x^2-9\right)=\left(x^2-9\right)\left(x^2+1\right)=\left(x-3\right)\left(x+3\right)\left(x^2+1\right)\)
A= \(\frac{13-x}{x+3}+\frac{6}{\left(x-3\right)\left(x+3\right)}-\frac{3}{x+3}-\frac{2}{x-3}=0\) \(\Leftrightarrow\frac{10-x}{x+3}+\frac{6}{\left(x-3\right)\left(x+3\right)}-\frac{2}{x-3}=0\) \(\Leftrightarrow\left(10x-30\right)\left(x-3\right)+6-2\left(x+3\right)=0\Leftrightarrow-x^2+11x-30=0\) \(\Leftrightarrow\left[\begin{array}{nghiempt}x=6\\x=5\end{array}\right.\)
LC
23 tháng 5 2016
ĐK: \(x\ne-3,3,-2\)
Ta có: \(\frac{13-x}{x+3}+\frac{6x^2+6}{x^4-8x^2-9}-\frac{3x+6}{x^2+5x+6}-\frac{2}{x-3}=0\)
=>\(\frac{13-x}{x+3}+\frac{6x^2+6}{x^4-9x^2+x^2-9}-\frac{3x+6}{x^2+3x+2x+6}-\frac{2}{x-3}=0\)
=>\(\frac{13-x}{x+3}+\frac{6x^2+6}{x^2.\left(x^2-9\right)+\left(x^2-9\right)}-\frac{3x+6}{x.\left(x+3\right)+2.\left(x+3\right)}-\frac{2}{x-3}=0\)
=>\(\frac{13-x}{x+3}+\frac{6.\left(x^2+1\right)}{\left(x^2+1\right).\left(x^2-9\right)}-\frac{3.\left(x+2\right)}{\left(x+2\right).\left(x+3\right)}-\frac{2}{x-3}=0\)
=>\(\frac{13-x}{x+3}+\frac{6}{x^2-9}-\frac{3}{x+3}-\frac{2}{x-3}=0\)
=>\(\left(\frac{13-x}{x+3}-\frac{3}{x+3}\right)+\left(\frac{6}{x^2-9}-\frac{2}{x-3}\right)=0\)
=>\(\frac{13-x-3}{x+3}+\left[\frac{6}{x^2-9}-\frac{2.\left(x+3\right)}{\left(x-3\right).\left(x+3\right)}\right]=0\)
=>\(\frac{10-x}{x+3}+\left[\frac{6}{x^2-9}-\frac{2x+6}{x^2-9}\right]=0\)
=>\(\frac{10-x}{x+3}+\frac{6-2x-6}{x^2-9}=0\)
=>\(\frac{\left(10-x\right).\left(x-3\right)}{\left(x+3\right).\left(x-3\right)}+\frac{-2x}{x^2-9}=0\)
=>\(\frac{13x-x^2-30}{x^2-9}-\frac{2x}{x^2-9}=0\)
=>\(\frac{13x-x^2-30-2x}{x^2-9}=0\)
=>\(\frac{11x-x^2-30}{x^2-9}=0\)
Vì \(x\ne-3,3=>x^2\ne0\)
=>11x-x2-30=0
=>6x-30-x2+5x=0
=>6.(x-5)-x.(x-5)=0
=>(6-x).(x-5)=0
=>6-x=0=>x=6
hoặc x-5=0=>x=5
Vậy tập nghiệm của phương trình S=6; 5
NP
2
Y
8 tháng 4 2019
+ Đặt \(t=x^2-3x+3\) thì pt đã cho trở thành :
\(\frac{1}{t}+\frac{2}{t+1}=\frac{6}{t+2}\)
\(\Leftrightarrow\frac{t+1+2t}{t\left(t+1\right)}=\frac{6}{t+2}\) \(\Leftrightarrow\frac{3t+1}{t^2+t}=\frac{6}{t+2}\)
\(\Leftrightarrow\left(3t+1\right)\left(t+2\right)=6\left(t^2+t\right)\)
\(\Leftrightarrow3t^2+7t+2=6t^2+6t\)
\(\Leftrightarrow3t^2-t-2=0\)
\(\Leftrightarrow3t^2-3t+2t-2=0\)
\(\Leftrightarrow\left(3t+2\right)\left(t-1\right)=0\)
\(\Leftrightarrow t-1=0\) ( do \(3t+2=3x^2-9x+11\)\(=3\left(x^2-2\cdot x\cdot\frac{3}{2}+\frac{9}{4}+\frac{17}{12}\right)=3\left[\left(x-\frac{3}{2}\right)^2+\frac{17}{12}\right]>0\forall x\))
\(\Leftrightarrow x^2-3x+3=1\)
\(\Leftrightarrow\left(x-\frac{3}{2}\right)^2+\frac{3}{4}=1\)
\(\Leftrightarrow\left(x-\frac{3}{2}\right)^2=\frac{1}{4}\)
\(\Leftrightarrow\left[{}\begin{matrix}x-\frac{3}{2}=\frac{1}{2}\\x-\frac{3}{2}=-\frac{1}{2}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=1\end{matrix}\right.\left(TM\right)\)
Vậy tập nghiệm của pt đã cho là \(S=\left\{1;2\right\}\)
NV
Nguyễn Việt Lâm
Giáo viên
8 tháng 4 2019
\(\frac{1}{x^2-3x+3}-1+\frac{2}{x^2-3x+4}-1+2-\frac{6}{x^2-3x+5}=0\)
\(\Leftrightarrow\frac{-x^2+3x-2}{x^2-3x+3}+\frac{-x^2+3x-2}{x^2-3x+4}-\frac{2\left(-x^2+3x-2\right)}{x^2-3x+5}=0\)
\(\Leftrightarrow\left(-x^2+3x-2\right)\left(\frac{1}{x^2-3x+3}+\frac{1}{x^2-3x+4}-\frac{2}{x^2-3x+5}\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}-x^2+3x-2=0\left(1\right)\\\frac{1}{x^2-3x+3}+\frac{1}{x^2-3x+4}-\frac{2}{x^2-3x+5}=0\left(2\right)\end{matrix}\right.\)
\(\left(1\right)\Leftrightarrow\left[{}\begin{matrix}x=2\\x=1\end{matrix}\right.\)
\(\left(2\right)\Leftrightarrow\frac{1}{x^2-3x+3}+\frac{1}{x^2-3x+4}-\frac{2}{x^2-3x+5}=0\)
Do \(\left\{{}\begin{matrix}\frac{1}{x^2-3x+3}>\frac{1}{x^2-3x+5}\\\frac{1}{x^2-3x+4}>\frac{1}{x^2-3x+5}\end{matrix}\right.\) \(\forall x\Rightarrow\frac{1}{x^2-3x+3}+\frac{1}{x^2-3x+4}-\frac{2}{x^2-3x+5}>0\)
\(\Rightarrow\left(2\right)\) vô nghiệm
KN
5 tháng 3 2020
\(\frac{3x-7}{5}=\frac{2x-1}{3}\)
\(\Leftrightarrow9x-21=10x-5\)
\(\Leftrightarrow-x=16\Leftrightarrow x=-16\)
\(\frac{4x-7}{12}-x=\frac{3x}{8}\)
\(\Leftrightarrow\frac{4x-7-12x}{12}=\frac{3x}{8}\)
\(\Leftrightarrow\frac{-7-8x}{12}=\frac{3x}{8}\)
\(\Leftrightarrow-56-64x=36x\)
\(\Leftrightarrow-56=100x\Leftrightarrow x=\frac{-14}{25}\)
KN
5 tháng 3 2020
\(\frac{x-2009}{1234}+\frac{x-2009}{5678}-\frac{x-2009}{197}=0\)
\(\Leftrightarrow\left(x-2019\right)\left(\frac{1}{1234}+\frac{1}{5678}-\frac{1}{197}\right)=0\)
Vì \(\left(\frac{1}{1234}+\frac{1}{5678}-\frac{1}{197}\right)\ne0\)nên x - 2019 = 0
Vậy x = 2019
\(\frac{5x-8}{3}=\frac{1-3x}{2}\)
\(\Leftrightarrow10x-16=3-9x\)
\(\Leftrightarrow19x=19\Leftrightarrow x=1\)
KC
1
NV
Nguyễn Việt Lâm
Giáo viên
15 tháng 3 2020
ĐKXĐ: ...
\(\Leftrightarrow\frac{2x}{x^2-3x+12}+\frac{6x}{x^2+2x+12}=1\)
\(\Leftrightarrow\frac{2}{x+\frac{12}{x}-3}+\frac{6}{x+\frac{12}{x}+2}=1\)
Đặt \(x+\frac{12}{x}-3=t\)
\(\Rightarrow\frac{2}{t}+\frac{6}{t+5}=1\Leftrightarrow2\left(t+5\right)+6t=t\left(t+5\right)\)
\(\Leftrightarrow t^2-3t-10=0\Rightarrow\left[{}\begin{matrix}t=5\\t=-2\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x+\frac{12}{x}-3=-2\\x+\frac{12}{x}-3=5\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x^2-x+12=0\\x^2-8x+12=0\end{matrix}\right.\) (casio)
NV
18 tháng 4 2017
\(1.\frac{7x-3}{x-1}=\frac{2}{3}\) ( \(x\ne1\))
\(\Leftrightarrow\frac{3\left(7x-1\right)}{3\left(x-1\right)}=\frac{2\left(x-1\right)}{3\left(x-1\right)}\)
\(\Rightarrow3\left(7x-3\right)=2\left(x-1\right)\)
\(\Leftrightarrow21x-9=2x-2\)
\(\Leftrightarrow19x=7\)
\(\Leftrightarrow x=\frac{7}{19}\)
\(2.\frac{5x-1}{3x+2}=\frac{5x-7}{3x-1}\)
\(\Leftrightarrow\frac{\left(5x-1\right)\left(3x-1\right)}{\left(3x+2\right)\left(3x-1\right)}=\frac{\left(5x-7\right)\left(3x+2\right)}{\left(3x-1\right)\left(3x+2\right)}\)
\(\Rightarrow\left(5x-1\right)\left(3x-1\right)=\left(5x-7\right)\left(3x+2\right)\)
\(\Leftrightarrow15x^2-5x-3x+1=15x^2+10x-21x-14\)
\(\Leftrightarrow15x^2-8x+1=15x^2-11x-14\)
\(\Leftrightarrow\left(15x^2-15x^2\right)+\left(-8x+11x\right)=-14-1\)
\(\Leftrightarrow3x=-15\)
\(\Leftrightarrow x=-5\)
\(3.\frac{1-x}{x+1}+3=\frac{2x+3}{3x-1}\)
\(\Leftrightarrow\frac{\left(1-x\right)\left(3x-1\right)}{\left(x+1\right)\left(3x-1\right)}+\frac{3\left(x+1\right)\left(3x-1\right)}{\left(x+1\right)\left(3x-1\right)}=\frac{\left(2x+3\right)\left(x+1\right)}{\left(3x-1\right)\left(0+1\right)}\)
\(\Rightarrow\left(1-x\right)\left(3x-1\right)+3\left(x+1\right)\left(3x-1\right)=\left(2x+3\right)\left(x+1\right)\)
\(\Leftrightarrow3x-1-3x^2+x+3\left(3x^2-x+3x-1\right)=2x^2+2x+3x+3\)
\(\Leftrightarrow3x-1-3x^2+x+9x^2-3x+9x-3=2x^2+2x+3x+3\)
\(\Leftrightarrow6x^2+10x-4=2x^2+5x+3\)
\(\Leftrightarrow\left(6x^2-2x^2\right)+\left(10x-5x\right)=7\)
\(\Leftrightarrow4x^2+5x-7=0\)
\(\Leftrightarrow\left(2x\right)^2+4x.\frac{5}{4}+\frac{16}{25}+\frac{191}{25}=0\)
\(\Leftrightarrow\left(2x+\frac{5}{4}\right)^2-\frac{191}{25}=0\)
\(\left(2x+\frac{5}{4}\right)^2>0\)
\(\Rightarrow\left(2x+\frac{5}{4}\right)^2+\frac{191}{25}>0\)
=> PT vô nghiệm
\(4.\frac{1-6x}{x-2}+\frac{9x+4}{x+2}=\frac{x\left(3x-2\right)+1}{x^2-4}\)
\(\Leftrightarrow\frac{\left(1-6x\right)\left(x+2\right)}{x^2-4}+\frac{\left(9x+4\right)\left(x-2\right)}{x^2-4}=\frac{2\left(3x-2\right)+1}{x^2-4}\)
\(\Rightarrow\left(1-6x\right)\left(x+2\right)+\left(9x+4\right)\left(x-2\right)=3\left(3x-2\right)+1\)
\(\Leftrightarrow x+2-6x^2-12x+9x^2-18x+4x-8=3x^2-2x+1\)
\(\Leftrightarrow3x^2-25x-6=3x^2-2x+1\)
\(\Leftrightarrow\left(3x^2-3x^2\right)+\left(-25x+2x\right)+\left(-6-1\right)=0\)
\(\Leftrightarrow-23x-7=0\)
\(\Leftrightarrow-23x=7\)
\(\Leftrightarrow x=\frac{-7}{23}\)
\(5.\frac{3x+2}{3x-2}-\frac{6}{2+3x}=\frac{9x^2}{9x^2-4}\)
\(\Leftrightarrow\frac{\left(3x+2\right)^2}{9x^2-4}-\frac{6\left(3x-2\right)}{9x^2-4}=\frac{9x^2}{9x^2-4}\)
\(\Rightarrow\left(3x+2\right)^2-6\left(3x-2\right)=9x^2\)
\(\Leftrightarrow9x^2+12x+4-18x+12=9x^2\)
\(\Leftrightarrow\left(9x^2-9x^2\right)+\left(12x-18x\right)+\left(4+12\right)=0\)
\(\Leftrightarrow-6x+16=0\)
\(\Leftrightarrow-6x=-16\)
\(\Leftrightarrow x=\frac{16}{6}\)
\(6.1+\frac{1}{x+2}=\frac{12}{8-x^3}\)
\(\Leftrightarrow\frac{\left(x+2\right)\left(8-x^3\right)}{\left(x+2\right)\left(8-x^3\right)}+\frac{1\left(8-x^3\right)}{\left(x+2\right)\left(8-x^3\right)}=\frac{12\left(x+2\right)}{\left(x+2\right)\left(8-x^3\right)}\)
\(\Rightarrow\left(x+2\right)\left(8-x^3\right)+1\left(8-x^3\right)=12\left(x+2\right)\)
\(\Leftrightarrow8x+x^4+16+2x^3+8-x^3=12x+24\)
\(\Leftrightarrow x^4+\left(2x^3-x^3\right)+\left(8x-12x\right)+\left(16-24\right)=0\)
\(\Leftrightarrow x^4+x^3-4x-8=0\)
\(\Leftrightarrow\left(x^4-4x\right)+\left(x^3-8\right)=0\)
Đến đấy mk tắc r xl bạn nhé
IA
1
16 tháng 3 2020
\(pt\Leftrightarrow\frac{2x}{x^2-3x+12}+\frac{6x}{x^2+2x+12}=1\)
\(\Leftrightarrow\frac{2}{x-3+\frac{12}{x}}+\frac{6}{x+2+\frac{12}{x}}=1\)
Đặt \(x+\frac{12}{x}=t\)
Khi đó:
\(pt\Leftrightarrow\frac{2}{t-3}+\frac{6}{t+2}=1\Leftrightarrow2t+4+6t-18=t^2-t-6\)
\(\Leftrightarrow t^2-t-6=8t-14\)
\(\Leftrightarrow t^2-9t+8=0\)
\(\Leftrightarrow\left(t-8\right)\left(t-1\right)=0\)
\(\Leftrightarrow x+\frac{12}{x}=8;x+\frac{12}{x}=1\)
Thôi,bí rồi
Đặt x2-3x+4=a
=>\(\frac{1}{a-1}+\frac{2}{a}=\frac{6}{a+1}\)
ĐKXĐ:a khác 1 ; -1 ;0
=>a2+a+2a2-2=6a2-6a
<=>6a2-3a2-a-6a+2=0
<=>3a2-7a+2=0
<=>(3a-1)(a-2)=0
<=>a=1/3 hoặc a=2
*)a=1/3
=>x2-3x+4=1/3
<=>x2-3x+11/3=0
<=>(x-1,5)2+17/12=0(vô lí)
*)a=2
=>x2-3x+4=2
<=>x2-3x+2=0
<=>(x-1)(x-2)=0
<=>x=1 hoặc x=2
Vậy x={1;2}