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`9/[x^2-4]=[x-1]/[x+2]+3/[x-2]` `ĐK: x \ne +-2`
`<=>9/[(x-2)(x+2)]=[(x-1)(x-2)+3(x+2)]/[(x-2)(x+2)]`
`=>9=x^2-2x-x+2+3x+6`
`<=>x^2=1`
`<=>x=+-1` (t/m)
Vậy `x=+-1`
\(\dfrac{9}{x^2-4}=\dfrac{x-1}{x+2}+\dfrac{3}{x-2}\left(đkxđ:x\ne\pm2\right)\\ \Leftrightarrow\dfrac{9}{\left(x-2\right)\left(x+2\right)}=\dfrac{\left(x-1\right)\left(x-2\right)}{\left(x-2\right)\left(x+2\right)}+\dfrac{3\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}\\ \Rightarrow9=x^2-3x+2+3x+6\\ \Leftrightarrow x^2=1\\ \Leftrightarrow x^2=\pm1\left(TM\right)\)
Vậy PT có tập nghiệm \(S=\left\{-1;1\right\}\)
`(x+19)/3 +(x+13)/5 = (x+7)/7 + (x+1)/9`
`<=> x/3 + 19/3 +x/5 +13/5 = x/7 +1 +x/9 +1/9`
`<=> x/3 +x/5 -x/7 -x/9 = 1+1/9 -19/3 -13/5`
`<=> x (1/3 +1/5 -1/7 -1/9) = -118/45`
`<=> x * 88/315 = -352/45`
`<=> x = -28`
Vậy `S={-28}`
Ta có : \(x^2+x+4=x^2+x+\frac{1}{4}+\frac{15}{4}=\left(x+\frac{1}{2}\right)^2+\frac{15}{4}>0\left(\forall x\right)\)
+) \(\left(x-1\right)\left(x^2+x+4\right)=0\)
\(\Leftrightarrow x-1=0\Leftrightarrow x=1\)
\(\left(x-1\right)\left(x^2+x+4\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x-1=0\\x^2+x+4=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=1\\x^2+x=-4\end{cases}}\)
+) x2 + x = - 4
<=> ( x + 1/2 )2 = - 4 + 1/4 = -15/4
Mà ( x + 1/2 )2 lớn hơn hoặc bằng 0 với mọi x
=> x2 + x + 4 = 0 ktm
Vậy pt = 0 <=> x = 1
\(1,\dfrac{3x+2}{6}-\dfrac{3x-2}{4}=\dfrac{15}{8}\\ \Leftrightarrow\dfrac{4\left(3x+2\right)}{24}-\dfrac{6\left(3x-2\right)}{24}-\dfrac{45}{24}=0\\ \Leftrightarrow12x+24-18x+12-45=0\\ \Leftrightarrow-6x-9=0\\ \Leftrightarrow x=-\dfrac{3}{2}\)
2, ĐKXĐ:\(x\ne\pm3\)
\(\dfrac{x+2}{3+x}-\dfrac{x}{3-x}=\dfrac{8x-6}{9-x^2}\\ \Leftrightarrow\dfrac{\left(x+2\right)\left(3-x\right)}{\left(3+x\right)\left(3-x\right)}-\dfrac{x\left(3+x\right)}{\left(3+x\right)\left(3-x\right)}-\dfrac{8x-6}{\left(3+x\right)\left(3-x\right)}=0\\ \Leftrightarrow\dfrac{-x^2+x+6-3x-x^2-8x+6}{\left(3+x\right)\left(3-x\right)}=0\\ \Leftrightarrow-2x^2-10x+12=0\\ \Leftrightarrow x^2+5x-6=0\\ \Leftrightarrow\left(x-1\right)\left(x+6\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=1\left(tm\right)\\x=-6\left(tm\right)\end{matrix}\right.\)
\(a,\dfrac{3x+2}{6}-\dfrac{3x-2}{4}=\dfrac{15}{8}\)
\(\Leftrightarrow4\left(3x+2\right)-6\left(3x-2\right)=45\)
\(\Leftrightarrow12x+8-18x+12=45\)
\(\Leftrightarrow12x-18x=45-12-8\)
\(\Leftrightarrow-6x=25\)
\(\Leftrightarrow x=\dfrac{-25}{6}\)
Vậy \(S=\left\{\dfrac{-25}{6}\right\}\)
\(b,\dfrac{x+2}{3+x}-\dfrac{x}{3-x}=\dfrac{8x-6}{9-x^2}\left(ĐKXĐ:x\ne3;x\ne-3\right)\)
\(\Leftrightarrow\left(x+2\right)\left(3-x\right)-x\left(3+x\right)=8x-6\)
\(\Leftrightarrow3x-x^2+6-2x-3x-x^2=8x-6\)
\(\Leftrightarrow-x^2-x^2+3x-2x-3x-8x=-6+6\)
\(\Leftrightarrow-2x^2-10x=0\)
\(\Leftrightarrow-2x\left(x-5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}-2x=0\\x-5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\left(nhận\right)\\x=5\left(nhận\right)\end{matrix}\right.\)
Vậy \(S=\left\{0;5\right\}\)
bai 1
1 thay k=0 vao pt ta co 4x^2-25+0^2+4*0*x=0
<=>(2x)^2-5^2=0
<=>(2x+5)*(2x-5)=0
<=>2x+5=0 hoăc 2x-5 =0 tiếp tục giải ý 2 tương tự
\(\Leftrightarrow3x+6+x^2-3x+2=9\)
\(\Leftrightarrow x^2+8=9\)
hay \(x\in\left\{1;-1\right\}\)
ĐKXĐ:\(x\ne\pm2\)
\(\dfrac{3}{x-2}+\dfrac{x-1}{x+2}=\dfrac{9}{x^2-4}\\ \Leftrightarrow\dfrac{3\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}+\dfrac{\left(x-1\right)\left(x-2\right)}{\left(x-2\right)\left(x+2\right)}-\dfrac{9}{\left(x-2\right)\left(x+2\right)}=0\\ \Leftrightarrow\dfrac{3\left(x+2\right)+\left(x-1\right)\left(x-2\right)-9}{\left(x-2\right)\left(x+2\right)}=0\\ \Rightarrow3\left(x+2\right)+\left(x-1\right)\left(x-2\right)-9=0\\ \Leftrightarrow3x+6+x^2-x-2x+2-9=0\\ \Leftrightarrow x^2-1=0\\ \Leftrightarrow\left(x-1\right)\left(x+1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=-1\left(tm\right)\\x=1\left(tm\right)\end{matrix}\right.\)
a) \(2\left(x+5\right)-x^2-5x=0\)
\(\Leftrightarrow2x+10-x^2-5x=0\)
\(\Leftrightarrow-x^2-3x+10=0\)
\(\Leftrightarrow x^2+3x-10=0\)
\(\Leftrightarrow x^2-2x+5x-10=0\)
\(\Leftrightarrow x\left(x-2\right)+5\left(x-2\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x+5\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x-2=0\\x+5=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=2\\x=-5\end{cases}}}\)
b) \(x^3-6x^2+12x-8=0\)
\(\Leftrightarrow\left(x^3-8\right)-\left(6x^2-12x\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x^2+2x+4\right)-6x\left(x-2\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x^2+2x+4-6x\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x^2-4x+4\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x-2\right)^2=0\)
\(\Leftrightarrow\left(x-2\right)^3=0\)
\(\Leftrightarrow x-2=0\Leftrightarrow x=2\)
c)\(16x^2-9\left(x+1\right)^2=0\)
\(\Leftrightarrow\left(4x\right)^2-\left[3\left(x+1\right)\right]^2=0\)
\(\Leftrightarrow\left(4x-3x-1\right)\left(4x+3x+1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(7x+1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x-1=0\\7x+1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=1\\x=-\frac{1}{7}\end{cases}}}\)
d) \(x^3+x=0\)
\(\Leftrightarrow x^2\left(x+1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x^2=0\\x+1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=0\\x=-1\end{cases}}}\)
e)\(x^2-2x-3=0\)
\(\Leftrightarrow x^2+x-3x-3=0\)
\(\Leftrightarrow x\left(x+1\right)-3\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(x-3\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x+1=0\\x-3=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-1\\x=3\end{cases}}}\)
`1/9(x-3)^2-1/25(x+5)^2=0`
`<=>(1/3x-1)^2-(1/5x+1)^2=0`
`<=>(1/3x-1-1/5x-1)(1/3x-1+1/5x+1)=0`
`<=>(2/15x-2). 8/15x=0`
`<=>2/15x-2=0` hoặc `8/15x=0`
`<=>x=15` hoặc `x=0`
Vậy `S=`{`15;0`}