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\(x^4-10x^3+35x^2+24>0\)
\(\Leftrightarrow x^4-2.5.x^3+\left(5x\right)^2+10x^2+24>0\)
\(\Leftrightarrow\left(x^2-5x\right)^2+10x^2+24>0\)
\(\Leftrightarrow x^2\left(x-5\right)^2+10x^2+24>0\)(luôn đúng)
Vậy nghiệm của bất phương trình \(x\in R\)
Câu 1:
a) Ta có: 7x+21=0
\(\Leftrightarrow7x=-21\)
hay x=-3
Vậy: S={-3}
b) Ta có: 3x-2=2x-3
\(\Leftrightarrow3x-2-2x+3=0\)
\(\Leftrightarrow x+1=0\)
hay x=-1
Vậy: S={-1}
c) Ta có: 5x-2x-24=0
\(\Leftrightarrow3x=24\)
hay x=8
Vậy: S={8}
Câu 2:
a) Ta có: \(\left(2x+1\right)\left(x-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}2x+1=0\\x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=-1\\x=1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=1\end{matrix}\right.\)
Vậy: \(S=\left\{-\dfrac{1}{2};1\right\}\)
b) Ta có: \(\left(2x-3\right)\left(-x+7\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}2x-3=0\\-x+7=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=3\\-x=-7\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=7\end{matrix}\right.\)
Vậy: \(S=\left\{\dfrac{3}{2};7\right\}\)
c) Ta có: \(\left(x+3\right)^3-9\left(x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left[\left(x+3\right)^2-9\right]=0\)
\(\Leftrightarrow\left(x+3\right)\left(x+3-3\right)\left(x+3+3\right)=0\)
\(\Leftrightarrow x\left(x+3\right)\left(x+6\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x+3=0\\x+6=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-3\\x=-6\end{matrix}\right.\)
Vậy: S={0;-3;-6}
b: ĐKXD: x<>1/5; x<>3
PT\(\Leftrightarrow\dfrac{3}{5x-1}-\dfrac{2}{x-3}=\dfrac{-4}{\left(5x-1\right)\left(x-3\right)}\)
=>3x-9-10x+2=-4
=>-7x-7=-4
=>-7x=3
=>x=-3/7
a: ĐKXĐ: x<>2/3; x<>-2/3
\(PT\Leftrightarrow\left(3x+2\right)^2-6\left(3x-2\right)=9x\)
=>9x^2+12x+4-18x+12-9x=0
=>9x^2-15x+16=0
=>\(x\in\varnothing\)
c: ĐKXĐ: x<>1/4; x<>-1/4
PT =>-3(4x+1)=2(4x-1)-6x-8
=>-12x-3=8x-2-6x-8
=>-12x-3=2x-10
=>-14x=-7
=>x=1/2
d: ĐKXĐ: x<>0; x<>2
\(\Leftrightarrow\dfrac{5-x}{4x\left(x-2\right)}+\dfrac{7}{8x}=\dfrac{x-1}{2x\left(x-2\right)}+\dfrac{1}{8\left(x-2\right)}\)
=>2(5-x)+7(x-2)=4(x-1)+x
=>10-2x+7x-14=4x-4+x
=>5x-4=5x-4
=>0x=0(luôn đung)
Vậy: S=R\{0;2}
e: DKXĐ: x<>0
PT \(\Leftrightarrow\dfrac{\left(x+1\right)\left(x^2-x+1\right)-\left(x-1\right)\left(x^2+x+1\right)}{\left(x^2+x+1\right)\left(x^2-x+1\right)}=\dfrac{3}{x\left(x^2+x+1\right)\left(x^2-x+1\right)}\)
=>x(x^3+1-x^3+1)=3
=>2x=3
=>x=3/2
\(a,\dfrac{y-1}{y-2}-\dfrac{5}{y+2}=\dfrac{12}{y^2-4}+1\left(ĐKXĐ:x\ne\pm2\right)\)
\(\Leftrightarrow\dfrac{\left(y-1\right)\left(y+2\right)}{\left(y-2\right)\left(y+2\right)}-\dfrac{5\left(y-2\right)}{\left(y-2\right)\left(y+2\right)}-\dfrac{12}{\left(y-2\right)\left(y+2\right)}-\dfrac{\left(y-2\right)\left(y+2\right)}{\left(y-2\right)\left(y+2\right)}=0\)
\(\Leftrightarrow\dfrac{y^2+y-2}{\left(y-2\right)\left(y+2\right)}-\dfrac{5y-10}{\left(y-2\right)\left(y+2\right)}-\dfrac{12}{\left(y-2\right)\left(y+2\right)}-\dfrac{y^2-4}{\left(y-2\right)\left(y+2\right)}=0\)
\(\Leftrightarrow\dfrac{y^2+y-2-5y+10-12-y^2+4}{\left(y-2\right)\left(y+2\right)}=0\)
\(\Rightarrow-4y=0\)
\(\Leftrightarrow y=0\left(tm\right)\)
\(b,\dfrac{1}{4z^2-12z+9}-\dfrac{3}{9-4z^2}=\dfrac{4}{4z^2+12z+9}\left(ĐKXĐ:z\ne\pm\dfrac{3}{2}\right)\)
\(\Leftrightarrow\dfrac{1}{\left(2z-3\right)^2}+\dfrac{3}{\left(2z-3\right)\left(2z+3\right)}-\dfrac{4}{\left(2z+3\right)^2}=0\)
\(⇔\dfrac{\left(2z+3\right)^2}{\left(2z-3\right)^2\left(2z+3\right)^2}+\dfrac{3\left(2z-3\right)\left(2z+3\right)}{\left(2z-3\right)^2\left(2z+3\right)^2}-\dfrac{4\left(2z-3\right)^2}{\left(2z-3\right)^2\left(2z+3\right)^2}=0\)
\(\Leftrightarrow\dfrac{4z^2+12z+9}{\left(2z-3\right)^2\left(2z+3\right)^2}+\dfrac{12z^2-27}{\left(2z-3\right)^2\left(2z+3\right)^2}-\dfrac{16z^2-48z+36}{\left(2z-3\right)^2\left(2z+3\right)^2}=0\)
\(\Leftrightarrow\dfrac{4z^2+12z+9+12z^2-27-16z^2+48z-36}{\left(2z-3\right)^2\left(2z+3\right)^2}=0\)
\(\Rightarrow60z-54=0\)
\(\Leftrightarrow60z=54\)
\(\Leftrightarrow z=\dfrac{9}{10}\left(tm\right).\)
\(a,\dfrac{y-1}{y-2}-\dfrac{5}{y+2}=\dfrac{12}{y^2-4}+1\left(dkxd:y\ne\pm2\right)\)
\(\Leftrightarrow\dfrac{\left(y-1\right)\left(y+2\right)-5\left(y-2\right)-12-y^2+4}{y^2-4}=0\)
\(\Leftrightarrow y^2+2y-y-2-5y+10-12-y^2+4=0\)
\(\Leftrightarrow-4y=0\)
\(\Leftrightarrow y=0\left(tmdk\right)\)
Vậy \(S=\left\{0\right\}\)
\(b,\dfrac{1}{4z^2-12z+9}-\dfrac{3}{9-4z^2}=\dfrac{4}{4z^2+12z+9}\)
\(\Leftrightarrow\dfrac{1}{\left(2z-3\right)^2}-\dfrac{3}{\left(2z-3\right)\left(2z+3\right)}=\dfrac{4}{\left(2z+3\right)^2}\left(dkxd:z\ne\pm\dfrac{3}{2}\right)\)
\(\Leftrightarrow\left(2z+3\right)^2-3\left(4z^2-9\right)-4\left(2z-3\right)^2=0\)
\(\Leftrightarrow4z^2+12z+9-12z^2+27-4\left(4z^2-12z+9\right)=0\)
\(\Leftrightarrow4z^2+12z+9-12z^2+27-16z^2+48z-36=0\)
\(\Leftrightarrow-24z^2+60z=0\)
\(\Leftrightarrow-12z\left(2z-5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}-12z=0\\2z-5=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}z=0\left(tmdk\right)\\z=\dfrac{5}{2}\left(tmdk\right)\end{matrix}\right.\)
Vậy \(S=\left\{0;\dfrac{5}{2}\right\}\)
1: \(=\dfrac{-\left[\left(x+5\right)^2-9\right]}{\left(x+2\right)^2}=\dfrac{-\left(x+5-3\right)\left(x+5+3\right)}{\left(x+2\right)^2}\)
\(=\dfrac{-\left(x+2\right)\left(x+8\right)}{\left(x+2\right)^2}=\dfrac{-\left(x+8\right)}{x+2}\)
2: \(=\dfrac{2x\left(x^2-4x+16\right)}{\left(x+4\right)\left(x^2-4x+16\right)}=\dfrac{2x}{x+4}\)
3: \(=\dfrac{5x\left(x^2+1\right)}{\left(x^2-1\right)\left(x^2+1\right)}=\dfrac{5x}{x^2-1}\)
4: \(=\dfrac{3\left(x^2-4x+4\right)}{x\left(x^3-8\right)}=\dfrac{3\left(x-2\right)^2}{x\left(x-2\right)\left(x^2+2x+4\right)}\)
\(=\dfrac{3\left(x-2\right)}{x\left(x^2+2x+4\right)}\)
5: \(=\dfrac{2a\left(a-b\right)}{a\left(c+d\right)-b\left(c+d\right)}=\dfrac{2a\left(a-b\right)}{\left(c+d\right)\left(a-b\right)}=\dfrac{2a}{c+d}\)
6: \(=\dfrac{x\left(x-y\right)}{\left(x-y\right)\left(x+y\right)}\cdot\left(-1\right)=\dfrac{-x}{x+y}\)
7: \(=\dfrac{2\left(1-a\right)}{-\left(1-a^3\right)}=\dfrac{-2\left(1-a\right)}{\left(1-a\right)\left(1+a+a^2\right)}=-\dfrac{2}{1+a+a^2}\)
8: \(=\dfrac{x^4\left(x^3-1\right)}{\left(x^3-1\right)\left(x^3+1\right)}=\dfrac{x^4}{x^3+1}\)
9: \(=\dfrac{\left(x+2-x+2\right)\left(x+2+x-2\right)}{16x}=\dfrac{4\cdot2x}{16x}=\dfrac{1}{2}\)
10: \(=\dfrac{0.5\left(49x^2-y^2\right)}{0.5x\left(7x-y\right)}=\dfrac{1}{x}\cdot\dfrac{\left(7x-y\right)\left(7x+y\right)}{7x-y}\)
\(=\dfrac{7x+y}{x}\)
ĐKXĐ:\(x\ne-2\)
\(\dfrac{1}{x+2}-1=\dfrac{5x+7}{x+2}\\ \Leftrightarrow\dfrac{1}{x+2}-\dfrac{5x+7}{x+2}=1\\ \Leftrightarrow\dfrac{1-5x-7}{x+2}=1\\ \Leftrightarrow-5x-6=x+2\\ \Leftrightarrow x+2+5x+6=0\\ \Leftrightarrow6x+8=0\\ \Leftrightarrow x=-\dfrac{4}{3}\left(tm\right)\)
thank
Để \(2x^3-4x^2+6x+a⋮x+2\)
\(\Leftrightarrow2x^3-4x^2+6x+a=\left(x+2\right)\cdot a\left(x\right)\)
Thay \(x=-2\)
\(\Leftrightarrow2\left(-2\right)^3-4\left(-2\right)^2+6\left(-2\right)+a=0\\ \Leftrightarrow-16-16-12+a=0\\ \Leftrightarrow-44+a=0\Leftrightarrow a=44\)
+)x=0 khong phai la nghiem cua phuong trinh
+)chia ca 2 ve cho \(x^2\ne\) 0 ta co:
\(x^2-5x+8-\frac{5}{x}+\frac{1}{x^2}=0\)
\(\Leftrightarrow\left(x^2+\frac{1}{x^2}\right)-5\left(x+\frac{1}{x}\right)+8=0\) (1)
Dat \(x+\frac{1}{x}=a\) \(\left(\left|a\right|\ge2\right)\)
\(\Rightarrow\)\(x^2+\frac{1}{x^2}=a^2-2\)
(1)\(\Leftrightarrow\)\(\left(a^2-2\right)-5a+8=0\)
den day ban tu giai tiep nhe