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24 tháng 3 2020
a) 7x - 35 = 0
<=> 7x = 0 + 35
<=> 7x = 35
<=> x = 5
b) 4x - x - 18 = 0
<=> 3x - 18 = 0
<=> 3x = 0 + 18
<=> 3x = 18
<=> x = 5
c) x - 6 = 8 - x
<=> x - 6 + x = 8
<=> 2x - 6 = 8
<=> 2x = 8 + 6
<=> 2x = 14
<=> x = 7
d) 48 - 5x = 39 - 2x
<=> 48 - 5x + 2x = 39
<=> 48 - 3x = 39
<=> -3x = 39 - 48
<=> -3x = -9
<=> x = 3
NN
7 tháng 4 2019
\(\frac{2x}{5}+\frac{3-2x}{3}\ge\frac{3x+2}{2}\)
\(\Leftrightarrow\)\(\frac{12x}{30}+\frac{10\left(3-2x\right)}{30}\ge\frac{15\left(3x+2\right)}{30}\)
\(\Leftrightarrow\)12x + 30 - 20x \(\ge\) 45x + 30
\(\Leftrightarrow\) 12x - 20x - 45x \(\ge\) -30 + 30
\(\Leftrightarrow\)- 53x \(\ge\)0
\(\Leftrightarrow\)x \(\le\)0
Vậy bất phương trình có nghiệm là : x \(\le0\)
b) \(1-\frac{2x-5}{6}>\frac{3-x}{4}\)
\(\Leftrightarrow\)\(\frac{12}{12}-\frac{2\left(2x-5\right)}{12}>\frac{3\left(3-x\right)}{12}\)
\(\Leftrightarrow\) 12 - 4x + 10 > 9 - 3x
\(\Leftrightarrow\)-4x + 3x > -12 - 10 + 9
\(\Leftrightarrow\)-x > -13
\(\Leftrightarrow\)x < 13
Vậy bất phương trình có nghiệm là : x < 13
BT
0
WR
11 tháng 6 2017
1)
a) \(\frac{x+5}{3x-6}-\frac{1}{2}=\frac{2x-3}{2x-4}< =>\frac{2\left(x+5\right)}{2\left(3x-6\right)}-\frac{3x-6}{2\left(3x-6\right)}=\frac{3\left(2x-3\right)}{3\left(2x-4\right)}.\)
(đk:x khác \(\frac{1}{2}\))
\(\frac{2x+10}{6x-12}-\frac{3x-6}{6x-12}=\frac{6x-9}{6x-12}< =>2x+10-3x+6=6x-9< =>x=\frac{25}{7}\)
Vậy x=\(\frac{25}{7}\)
b) /7-2x/=x-3 \(x\ge\frac{7}{2}\)
(đk \(x\ge3,\frac{7}{2}< =>x\ge\frac{7}{2}\))
\(\Rightarrow\orbr{\begin{cases}7-2x=x-3\\7-2x=-\left(x-3\right)\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{10}{3}\left(< \frac{7}{2}\Rightarrow l\right)\\x=4\left(tm\right)\end{cases}}}\)
Vậy x=4
2)
\(\frac{x-1}{2}+\frac{x-2}{3}+\frac{x-3}{4}>\frac{x-4}{5}+\frac{x-5}{6}\)
\(\Leftrightarrow\frac{30\left(x-1\right)}{60}+\frac{20\left(x-2\right)}{60}+\frac{15\left(x-3\right)}{60}-\frac{12\left(x-4\right)}{60}-\frac{10\left(x-5\right)}{60}>0\)
\(\Leftrightarrow30x-30+20x-40+15x-45-12x+48-10x+50>0\Leftrightarrow43x-17>0\Leftrightarrow x>\frac{17}{43}\)
6 tháng 6 2020
Bàii làm
a) ( x - 2 )( x - 3 ) = x2 - 4
<=> x2 - 2x - 3x + 6 = x2 - 4
<=> x2 - x2 - 5x + 6 - 4 = 0
<=> -5x + 2 = 0
<=> -5x = -2
<=> x = 2/5
Vậy x = 2/5 là nghiệm phương trình.
b) \(\frac{x+2}{x-2}-\frac{1}{x}=\frac{x+6}{x\left(x-2\right)}\)
=> x( x + 2 ) - ( x - 2 ) = x + 6
<=> x2 + 2x - x + 2 - x - 6 = 0
<=> x2 - 4 = 0
<=> x2 = 4
<=> x = + 4
Vậy nghiệm S = { + 4 }
c) \(\frac{2x-1}{-3}>1\)
\(\Leftrightarrow\frac{2x-1}{-3}.\left(-3\right)< 1\left(-3\right)\)
\(\Leftrightarrow2x-1< -3\)
\(\Leftrightarrow2x< -2\)
\(\Leftrightarrow x< -1\)
Vậy nghiệm bất phương trình S = { x / x < -1 }
d) ( x - 1 )2 < 5 - 2x
<=> x2 - 2x + 1 < 5 - 2x
<=> x2 - 2x + 1 - 5 + 2x < 0
<=> x2 - 4 < 0
<=> x2 < 4
<=> x < + 2
Vậy tập nghiệm S = { x / x < +2 }
TH
23 tháng 3 2019
a) \(\frac{x-1}{2}+\frac{x-2}{3}+\frac{x-3}{4}=\frac{x-4}{5}+\frac{x-5}{6}\)
\(\left(\frac{x-1}{2}+1\right)+\left(\frac{x-2}{3}+3\right)+\left(\frac{x-3}{4}+1\right)=\left(\frac{x-4}{5}+1\right)+\left(\frac{x-5}{6}+1\right)\)
\(\frac{x-1}{2}+\frac{x-1}{3}+\frac{x-1}{4}=\frac{x-1}{5}+\frac{x-1}{6}\)
\(\left(x-1\right)\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{1}{6}\right)\)=0
\(x-1=0\)
\(x=1\)
20 tháng 7 2019
\(\text{a) }\frac{6}{x-4}-\frac{x}{x+2}=\frac{6}{x-4}.\frac{x}{x+2}\)
\(ĐKXĐ:x\ne-2;x\ne4\)
\(MTC:\left(x-4\right)\left(x+2\right)\)
\(\Leftrightarrow\frac{6\left(x+2\right)}{\left(x-4\right)\left(x+2\right)}-\frac{x\left(x-4\right)}{\left(x-4\right)\left(x+2\right)}=\frac{6x}{\left(x-4\right)\left(x+2\right)}\)
\(\Rightarrow6\left(x+2\right)-x\left(x-4\right)=6x\)
\(\Leftrightarrow6x+12-x^2+4x=6x\)
\(\Leftrightarrow6x+12-x^2+4x-6x=0\)
\(\Leftrightarrow-x^2+4x+12=0\)
\(\Leftrightarrow-\left(x^2-4x-12\right)=0\)
\(\Leftrightarrow x^2-4x-12=0\)
\(\Leftrightarrow x^2+2x-6x-12=0\)
\(\Leftrightarrow x\left(x+2\right)-6\left(x+2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-6\right)=0\)
\(\Leftrightarrow x=-2\left(\text{loại}\right)\text{ hoặc }x=6\left(\text{nhận}\right)\)
Vậy \(S=\left\{6\right\}\)
\(\text{b) }\frac{2x+3}{2x-1}=\frac{x-3}{x+5}\)
\(ĐKXĐ:x\ne\frac{1}{2};x\ne-5\)
\(\Leftrightarrow\left(2x+3\right)\left(x+5\right)=\left(2x-1\right)\left(x-3\right)\left[\text{Tỉ lệ thức}\right]\)
\(\Leftrightarrow2x^2+10x+3x+15=2x^2-6x-x+3\)
\(\Leftrightarrow2x^2+13x+15=2x^2-7x+3\)
\(\Leftrightarrow2x^2+13x-2x^2+7x=3-15\)
\(\Leftrightarrow20x=-12\)
\(\Leftrightarrow x=\frac{-12}{20}=\frac{-3}{5}\)
Vậy \(S=\left\{\frac{-3}{5}\right\}\)
Đặt \(y=x^2-2x+3=\left(x-1\right)^2+2\ge2\), ta có:
\(x^2-2x+3=\frac{6}{x^2-2x+4}\Leftrightarrow y=\frac{6}{y+1}\Leftrightarrow y\left(y+1\right)=6\Leftrightarrow y^2+y-6=0\)
\(\Leftrightarrow\left(y+3\right)\left(y-2\right)=0\Leftrightarrow\orbr{\begin{cases}y=2\\y=-3\end{cases}\Rightarrow y=2\Leftrightarrow\left(x-1\right)^2=0\Leftrightarrow x=1}\)
Vậy \(S=\left\{1\right\}\)