giải phương trình sau: 2x *(8x-1)^2 * (4x-1)=9 Cần gấp! cảm ơn mn
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Ta có: \(2x\left(8x-1\right)^2\left(4x-1\right)=9\)
=>\(\left(8x^2-2x\right)\left(64x^2-16x+1\right)=9\)
=>\(\left(8x^2-2x\right)\cdot\left\lbrack8\left(8x^2-2x\right)+1\right\rbrack-9=0\)
=>\(8\cdot\left(8x^2-2x\right)^2+\left(8x^2-2x\right)-9=0\)
=>\(8\cdot\left(8x^2-2x\right)^2+9\left(8x^2-2x\right)-8\left(8x^2-2x\right)-9=0\)
=>\(\left(8x^2-2x\right)\left\lbrack8\left(8x^2-2x\right)+9\right\rbrack-\left\lbrack8\left(8x^2-2x\right)+9\right\rbrack=0\)
=>\(\left(8x^2-2x-1\right)\left(64x^2-16x+9\right)=0\)
mà \(64x^2-16x+9=64x^2-2\cdot8x\cdot1+1+8=\left(8x-1\right)^2+8>0\forall x\)
nên \(8x^2-2x-1=0\)
=>\(8x^2-4x+2x-1=0\)
=>(2x-1)(4x+1)=0
=>\(\left[\begin{array}{l}2x-1=0\\ 4x+1=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac12\\ x=-\frac14\end{array}\right.\)
2x(8x-1)2(4x-1)= 9
<=> 2x(64x2-16x+1)(4x-1)=9
<=>(128x3 - 32x2 + 2x)(4x-1)=9
<=>512x4 - 256x3 + 40x2 - 2x=9
<=>64x4 - 32x3 + 5x2 - 0,25x - 1,125=0
<=>64x3(x-0,5) + 5x(x-0,5) + 2,5x -0,25x - 1,125 = 0
<=> (x-0,5)(64x3 + 5x - 2,25) = 0
<=> (x-0,5)(64x3 + 16x2 - 16x2 - 4x + 9x - 2,25)=0
<=>(x-0,5)[64x2 (x + 0,25 ) -16x(x + 0,25) + 9(x + 0,25) = 0
<=> (x-0,5)(x+0,25)(64x2 -16x +9) = 0 (vì 64x2 -16x +9 > 0)
<=>\(\orbr{\begin{cases}x-0,5=0\\x+0,25=0\end{cases}}\)
<=>\(\orbr{\begin{cases}x=0,5\\x=-0,25\end{cases}}\)
Vậy phương trình có hai nghiệm là S={\(\frac{1}{2}\) ; \(\frac{-1}{4}\)}
\(2x\left(8x-1\right)^2\left(4x-1\right)=9\)
\(\Leftrightarrow8x\left(8x-1\right)^2\left(8x-2\right)=72\)(nhân hai vế với 8)
Đặt \(8x-1=y\). Khi đó, pt được viết lại:
\(\left(y+1\right)y^2\left(y-1\right)=72\)
\(\Leftrightarrow y^2\left(y^2-1\right)=72\)
\(\Leftrightarrow y^4-y^2-72=0\)
\(\Leftrightarrow y^4+3y^3-3y^3-9y^2+8y^2+24y-24y-72=0\)
\(\Leftrightarrow y^3\left(y+3\right)-3y^2\left(y+3\right)+8y\left(y+3\right)-24\left(y+3\right)=0\)
\(\Leftrightarrow\left(y+3\right)\left(y^3-3y^2+8y-24\right)=0\)
\(\Leftrightarrow\left(y+3\right)\left(y^2\left(y-3\right)+8\left(y-3\right)\right)=0\)
\(\Leftrightarrow\left(y+3\right)\left(y-3\right)\left(y^2+8\right)=0\)
Mà \(y^2+8\ge8>0\)
\(\Rightarrow\orbr{\begin{cases}y+3=0\\y-3=0\end{cases}\Leftrightarrow\orbr{\begin{cases}y=-3\\y=3\end{cases}}}\)
TH1: \(y=-3\)
\(\Rightarrow8x-1=-3\)
\(\Leftrightarrow8x=-2\)
\(\Leftrightarrow x=\frac{-1}{4}\)
TH2: \(y=3\)
\(\Rightarrow8x-1=3\)
\(\Leftrightarrow8x=4\)
\(\Leftrightarrow x=\frac{1}{2}\)
Vậy tập nghiệm của pt là S={\(\frac{-1}{4};\frac{1}{2}\)}
a: ĐKXĐ: x<>4
Ta có: \(1+\frac{14}{\left(\left.x-4\right.\right)^2}=\frac{-9}{x-4}\)
=>\(\frac{\left(x-4\right)^2+14}{\left(x-4\right)^2}=\frac{-9\left(x-4\right)}{\left(x-4\right)^2}\)
=>\(\left(x-4\right)^2+14=-9\left(x-4\right)\)
=>\(\left(x-4\right)^2+9\left(x-4\right)+14=0\)
=>(x-4+2)(x-4+7)=0
=>(x-2)(x+3)=0
=>x=2(nhận) hoặc x=-3(nhận)
b: ĐKXĐ: x∉{1/2;-1/2}
Ta có: \(\frac{1+8x}{1+2x}-\frac{2x}{2x-1}+\frac{12x^2-9}{1-4x^2}=0\)
=>\(\frac{8x+1}{2x+1}-\frac{2x}{2x-1}-\frac{12x^2-9}{\left(2x-1\right)\left(2x+1\right)}=0\)
=>\(\frac{\left(8x+1\right)\left(2x-1\right)-2x\left(2x+1\right)-12x^2+9}{\left(2x-1\right)\left(2x+1\right)}=0\)
=>\(\left(8x+1\right)\left(2x-1\right)-2x\left(2x+1\right)-12x^2+9=0\)
=>\(16x^2-8x+2x-1-4x^2-2x-12x^2+9=0\)
=>-8x+8=0
=>-8x=-8
=>x=1(nhận)
c: ĐKXĐ: x∉{3;1}
\(\frac{1}{2x-6}-\frac{3x-5}{x^2-4x+3}=\frac12\)
=>\(\frac{1}{2\left(x-3\right)}-\frac{3x-5}{\left(x-1\right)\left(x-3\right)}=\frac12\)
=>\(\frac{x-1}{2\left(x-3\right)\left(x-1\right)}-\frac{2\left(3x-5\right)}{2\left(x-1\right)\left(x-3\right)}=\frac{x^2-4x+3}{2\left(x-1\right)\left(x-3\right)}\)
=>\(x^2-4x+3=x-1-2\left(3x-5\right)=x-1-6x+10=-5x+9\)
=>\(x^2+x-6=0\)
=>(x+3)(x-2)=0
=>x=-3(nhận) hoặc x=2(nhận)
Ta có: \(2x\left(8x-1\right)^2\left(4x-1\right)=9\)
=>\(\left(8x^2-2x\right)\left(64x^2-16x+1\right)=9\)
=>\(\left(8x^2-2x\right)\cdot\left\lbrack8\left(8x^2-2x\right)+1\right\rbrack-9=0\)
=>\(8\cdot\left(8x^2-2x\right)^2+\left(8x^2-2x\right)-9=0\)
=>\(8\cdot\left(8x^2-2x\right)^2+9\left(8x^2-2x\right)-8\left(8x^2-2x\right)-9=0\)
=>\(\left(8x^2-2x\right)\left\lbrack8\left(8x^2-2x\right)+9\right\rbrack-\left\lbrack8\left(8x^2-2x\right)+9\right\rbrack=0\)
=>\(\left(8x^2-2x-1\right)\left(64x^2-16x+9\right)=0\)
mà \(64x^2-16x+9=64x^2-2\cdot8x\cdot1+1+8=\left(8x-1\right)^2+8>0\forall x\)
nên \(8x^2-2x-1=0\)
=>\(8x^2-4x+2x-1=0\)
=>(2x-1)(4x+1)=0
=>\(\left[\begin{array}{l}2x-1=0\\ 4x+1=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac12\\ x=-\frac14\end{array}\right.\)