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NT
1
DL
6 tháng 2 2018
\(\left(x^2+8x+8\right)^2=\left(4x+6\right)\left(2x^2+12x+10\right)\)
\(\left(x^2+8x+8\right)^2-\left[\left(4x+6\right)\left(2x^2+12x+10\right)\right]=0\)
\(\left(x^2+4x+2\right)^2=0\)
\(x^2+4x=-2\)
\(x\left(x+4\right)=-2\)
\(x=\pm\sqrt{2}-2\)
VL
0
21 tháng 2 2019
\(\left(x-2\right)\left(x+2\right)\left(x^2-10\right)=72\)
<=>\(\left(x^2-4\right)\left(x^2-10\right)=72\) (1)
Đặt \(x^2-7=t\)
=> pt (1) <=> \(\left(t+3\right)\left(t-3\right)=72\)
<=> \(t^2-9=72\)
<=> \(t^2-81=0\)
<=> \(\left(t-9\right)\left(t+9\right)=0\)
Tự làm nốt
21 tháng 2 2019
\(8x^2-\left(4x+3\right)^3+\left(2x+3\right)^3=0\)
\(\Leftrightarrow8x^2+\left(2x+3-4x-3\right)\left[\left(4x+3\right)^2+\left(2x+3\right)\left(4x+3\right)+\left(2x+3\right)^2\right]=0\)
\(\Leftrightarrow8x^2-2x\left(16x^2+24x+9+8x^2+18x+9+4x^2+12x+9\right)=0\)
\(\Leftrightarrow2x\left(4x-28x^2-54x-27\right)=0\)
\(\Leftrightarrow2x\left(28x^2+50x+27\right)=0\)
Tự làm nốt
VN
16 tháng 8 2016
a) \(\frac{5-x}{4x^2-8x}\) + \(\frac{7}{8x}\) = \(\frac{x-1}{2x\left(x-2\right)}\) +\(\frac{1}{8x-16}\) ĐKXĐ : x #0, x#2, x#-2
<=> \(\frac{5-x}{4x\left(x-2\right)}\) + \(\frac{7}{8x}=\frac{x-1}{2x\left(x-2\right)}\) + \(\frac{1}{8\left(x-2\right)}\)
<=> \(\frac{2\left(5-x\right)}{8x\left(x-2\right)}+\frac{7\left(x-2\right)}{8x\left(x-2\right)}=\frac{4\left(x-1\right)}{8x\left(x-2\right)}+\frac{x}{8x\left(x-2\right)}\)
=> 10 - 2x + 7x - 14 = 4x - 4 + x
<=>-2x + 7x - 4x + x = -4 - 10 + 14
<=>x=-14
21 tháng 2 2019
\(a,x\left(x-1\right)\left(x+4\right)\left(x+5\right)=84\)
\(\Leftrightarrow\left[x\left(x+4\right)\right]\left[\left(x-1\right)\left(x+5\right)\right]=84\)
\(\Leftrightarrow\left(x^2+4x\right)\left(x^2+4x-5\right)=84\)
Đặt \(x^2+4x=a\)
Ta có : \(a=x^2+4x+4-4=\left(x+2\right)^2-4\ge-4\)
\(\Rightarrow a\ge-4\)
\(Ta\text{ }co'\text{ }pt:a\left(a-5\right)=84\)
\(\Leftrightarrow a^2-5a-84=0\)
\(\Leftrightarrow\left(a-12\right)\left(a+7\right)=0\)
Mà \(a\ge-4\Rightarrow a=12\)
\(\Rightarrow x^2+4x=12\)
\(\Leftrightarrow\left(x-2\right)\left(x+6\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x=2\\x=-6\end{cases}}\)
\(b,x^3-5x^2+8x-4=0\)
\(\Leftrightarrow\left(x-2\right)^2\left(x-1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x=2\\x=1\end{cases}}\)
14 tháng 2 2020
\(9x^2-1=\left(3x+1\right)\left(2x-3\right)\)
\(\Leftrightarrow\left(3x+1\right)\left(3x-1\right)=\left(3x+1\right)\left(2x-3\right)\)
\(\Leftrightarrow\left(3x+1\right)\left(3x-1\right)-\left(3x+1\right)\left(2x-3\right)=0\)
\(\Leftrightarrow\left(3x+1\right)\left(3x-1-2x+3\right)=0\)
\(\Leftrightarrow\left(3x+1\right)\left(x+2\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}3x+1=0\\x+2=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=\frac{-1}{3}\\x=-2\end{cases}}\)
14 tháng 2 2020
\(2\left(9x^2+6x+1\right)=\left(3x+1\right)\left(x-2\right)\)
\(\Leftrightarrow2\left(3x+1\right)^2=\left(3x+1\right)\left(x-2\right)\)
\(\Leftrightarrow2\left(3x+1\right)^2-\left(3x+1\right)\left(x-2\right)=0\)
\(\Leftrightarrow\left(3x+1\right)\left(6x+2-x+2\right)=0\)
\(\Leftrightarrow\left(3x+1\right)\left(5x+4\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}3x+1=0\\5x+4=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=\frac{-1}{3}\\x=\frac{-4}{5}\end{cases}}\)
\(\left(x^2+8x\right)+8\left(x^2+8x\right)=48\)
Đặt: \(u=x^2+8x\)
\(\Rightarrow u^2+8u=48\)
\(\Leftrightarrow u^2+8u-48=0\)
\(\Leftrightarrow u^2-4u+12u-48=0\)
\(\Leftrightarrow u\left(u-4\right)+12\left(u-4\right)=0\)
\(\Leftrightarrow\left(u+12\right)\left(u-4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}u+12=0\Leftrightarrow u=-12\\u-4=0\Leftrightarrow u=4\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x^2+8x=-12\\x^2+8x=4\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2+8x+12=0\\x^2+8x-4=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-4+2\sqrt{5}\\x=-4-2\sqrt{5}\\x=-2\\x=-6\end{matrix}\right.\)
\(\Leftrightarrow x^4+16x^3+64x^2+8x^2+64x=48\\ \Leftrightarrow x^4+16x^3+72x^2+64x-48=0\\ \Leftrightarrow\left(x+2\right)\left(x+6\right)\left(x^2+8x-4\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x+2=0\\x+6=0\\x^2+8x-4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=-6\\x=-4\pm2\sqrt{5}\end{matrix}\right.\)
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