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18 tháng 6 2022
a: \(\Leftrightarrow\dfrac{x+5}{2x-1}+\dfrac{2x-1}{x+5}-2=0\)
\(\Leftrightarrow\left(x+5\right)\left(x+5\right)+\left(2x-1\right)^2-2\left(2x-1\right)\left(x+5\right)=0\)
\(\Leftrightarrow x^2+10x+25+4x^2-4x+1-2\left(2x^2+10x-x-5\right)=0\)
\(\Leftrightarrow5x^2+6x+26-4x^2-18x+10=0\)
\(\Leftrightarrow x^2-12x+36=0\)
=>x=6
b: \(\dfrac{9x-27}{2x-7}-\dfrac{8x-28}{x-3}=0\)
\(\Leftrightarrow9\left(x-3\right)^2-4\left(2x-7\right)^2=0\)
\(\Leftrightarrow\left(3x-9\right)^2-\left(4x-14\right)^2=0\)
\(\Leftrightarrow\left(3x-9-4x+14\right)\left(3x-9+4x-14\right)=0\)
\(\Leftrightarrow\left(5-x\right)\left(7x-23\right)=0\)
hay \(x\in\left\{5;\dfrac{23}{7}\right\}\)
TI
1
BT
19 tháng 3 2018
a) \(x^5-27+x^3-27x^2\) = 0
\(\Leftrightarrow x^3\left(x^2+1\right)-27\left(x^2+1\right)\)= 0
\(\Leftrightarrow\left(x^2+1\right)\left(x^3-27\right)=0\)
\(\Leftrightarrow x^3-27=0\) (Vì \(x^2+1>0\))
\(\Leftrightarrow\left(x-3\right)\left(x^2+3x+9\right)=0\)
\(\Leftrightarrow\left(x-3\right)\left(x^2+2\dfrac{3}{2}x+\dfrac{9}{4}+\dfrac{27}{4}\right)=0\)
\(\Leftrightarrow\left(x-3\right)\left[\left(x+\dfrac{3}{2}\right)^2+\dfrac{27}{4}\right]=0\)
\(\Leftrightarrow x-3=0\) (Vì \(\left(x+\dfrac{3}{2}\right)^2+\dfrac{27}{4}>0\))
\(\Leftrightarrow x=3\)
Vậy tập nghiệm của phương trình là S = {3}
b)\(x^3-9x^2+19x-11=0\)
\(\Leftrightarrow\left(x^3-x^2\right)-\left(8x^2-8x\right)+\left(11x-11\right)=0\)
\(\Leftrightarrow x^2\left(x-1\right)-8x\left(x-1\right)+11\left(x-1\right)=0\)
\(\Leftrightarrow\)\(\left(x-1\right)\left(x^2-8x+11\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left[x^2-\left(4+\sqrt{5}\right)x-\left(4-\sqrt{5}\right)x+11\right]=0\)
\(\Leftrightarrow\left(x-1\right)\left\{x\left[x-\left(4+\sqrt{5}\right)\right]-\left(4-\sqrt{5}\right)\left[x-\left(4+\sqrt{5}\right)\right]\right\}=0\)
\(\Leftrightarrow\left(x-1\right)\left(x-4-\sqrt{5}\right)\left(x-4+\sqrt{5}\right)=0\)
\(\Leftrightarrow x-1=0\) hoặc \(x-4-\sqrt{5}=0\) hoặc \(x-4+\sqrt{5}=0\)
\(\Leftrightarrow x=1\) hoặc \(x=4+\sqrt{5}\) hoặc \(x=4-\sqrt{5}\)
Vậy phương trình có tập nghiệm là \(S=\left\{1;4+\sqrt{5};4-\sqrt{5}\right\}\)
8 tháng 2 2022
ĐKXĐ: \(x\ne\pm3\)
\(P=\left[\dfrac{x\left(x+3\right)}{x^2\left(x+3\right)+9\left(x+3\right)}+\dfrac{3}{x^2+9}\right]:\left[\dfrac{1}{x-3}-\dfrac{6x}{x^2\left(x-3\right)+9\left(x-3\right)}\right]\)
\(=\left[\dfrac{x\left(x+3\right)}{\left(x+3\right)\left(x^2+9\right)}+\dfrac{3}{x^2+9}\right]:\left[\dfrac{1}{x-3}-\dfrac{6x}{\left(x-3\right)\left(x^2+9\right)}\right]\)
\(=\dfrac{x+3}{x^2+9}:\dfrac{x^2+9-6x}{\left(x-3\right)\left(x^2+9\right)}=\dfrac{x+3}{x^2+9}.\dfrac{\left(x-3\right)\left(x^2+9\right)}{\left(x-3\right)^2}=\dfrac{x+3}{x-3}\)
Ý 2 mình k hiểu ý bạn lắm
\(P=\dfrac{x+3}{x-3}=\dfrac{x-3+6}{x-3}=1+\dfrac{6}{x-3}\in Z\)
\(\Leftrightarrow\left(x-3\right)\inƯ\left(6\right)=\left\{-6;-3;-2;-1;1;2;3;6\right\}\)
Kết hợp vs ĐKXĐ \(\Rightarrow x\in\left\{0;1;2;4;5;6;9\right\}\)
1 tháng 10 2018
d) x2(x−3)+27−9x=0
x2 (x - 3) + 27 - 9x = 0
x2 ( x - 3 ) +( 27 - 9x) = 0
x2 ( x - 3) + 9 ( 3 - x ) = 0
x2 ( x - 3) + 9 \(\left[-\left(x-3\right)\right]\) = 0
x2 ( x - 3) - 9 ( x - 3) = 0
(x - 3 )( x2 - 9) = 0
(x - 3) ( x-3) ( x + 3) = 0
(x - 3)2 ( x + 3) = 0
\(\Rightarrow\) x - 3 = 0 hoặc x+ 3 =0
+) x - 3 = 0 \(\Rightarrow\) x = 0+ 3=3
+) x+3= 0 \(\Rightarrow\) x = 0-3 = -3
Vậy: x= 3 hoặc x= -3
DV
10 tháng 12 2016
= \(\left[\frac{x.\left(x+3\right)}{\left(x+3\right).\left(x^2+9\right)}+\frac{3}{x+9}\right]:\left[\frac{1}{x-3}-\frac{6x}{\left(x-3\right)\left(x^2+9\right)}\right]\) ]
\(=\frac{x+3}{x^2-9}.\frac{\left(x-3\right).\left(x^2+9\right)}{x^2+9-6x}\)
= \(\frac{\left(x-3\right).\left(x+3\right)}{\left(x-3\right)^2}\)
= \(\frac{x+3}{x-3}\)
k mik nhé. Plssss~
DT
26 tháng 6 2016
\(\left(\frac{x^2+3x}{x^3+3x^2+9x+27}\right)\): \(\left(\frac{1}{x-3}-\frac{6x}{x^3-3x^2+9x-27}\right)\)
=\(\left[\frac{x\left(x+3\right)}{x^2\left(x+3\right)+9\left(x+3\right)}\right]\):\(\left[\frac{1}{x-3}-\frac{6x}{x^2\left(x-3\right)+9\left(x-3\right)}\right]\)
=\(\left[\frac{x\left(x-3\right)}{\left(x^2+9\right)\left(x-3\right)}\right]\):\(\left[\frac{1}{x-3}-\frac{6x}{\left(x^2+9\right)\left(x-3\right)}\right]\)
=\(\frac{x}{x^2+9}\):\(\left[\frac{x^2+9}{\left(x-3\right)\left(x^2+9\right)}-\frac{6x}{\left(x-3\right)\left(x^2+9\right)}\right]\)
=\(\frac{x}{x^2+9}\):\(\frac{\left(x-3\right)^2}{\left(x-3\right)\left(x^2+9\right)}\)
=\(\frac{x}{x^2+9}\):\(\frac{x-3}{x^2+9}\)
=\(\frac{x}{x^2+9}\).\(\frac{x^2+9}{x-3}\)
=\(\frac{x}{x-3}\)
DT
0
3 tháng 4 2020
<=> x^3 + x - 30 = 0
<=> x^3 - 3x^2 + 3x^2 - 9x + 10x - 30 = 0
<=> x^2(x-3) + 3x(x-3) + 10(x-3)=0
<=> (x-3)(x^2+3x+10) = 0
<=> x = 3 (vì x^2 + 3x + 10 > 0)
NT
3
1 tháng 10 2016
b) \(x^2-2x-3=0\)
\(D=b^2-4ac\)
\(\left(-2\right)^2-\left(4\left(1.3\right)\right)=16\)
\(x_{1,2}=\frac{-b-\sqrt{D}}{2a}=\frac{2-\sqrt{16}}{2}\)
\(x=1;-3\)
\(x^3+9x^2+27x+27=x^3+3x^2+6x^2+18x+9x+27=x^2\left(x+3\right)+6x\left(x+3\right)+9\left(x+3\right)\)
\(=\left(x^2+6x+9\right)\left(x+3\right)=\left(x+3\right)^2\left(x+3\right)=\left(x+3\right)^3=0\)
=>x+3=0=>x=-3