giải pt (3x+1)^2=3x+1
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ta có : x^5+2x^4+3x^3+3x^2+2x+1=0
\(\Leftrightarrow\)x^5+x^4+x^4+x^3+2x^3+2x^2+x^2+x+x+1=0
\(\Leftrightarrow\)(x^5+x^4)+(x^4+x^3)+(2x^3+2x^2)+(x^2+x)+(x+1)=0
\(\Leftrightarrow\)x^4(x+1)+x^3(x+1)+2x^2(x+1)+x(x+1)+(x+1)=0
\(\Leftrightarrow\)(x+1)(x^4+x^3+2x^2+x+1)=0
\(\Leftrightarrow\)(x+1)(x^4+x^3+x^2+x^2+x+1)=0
\(\Leftrightarrow\)(x+1)[x^2(x^2+x+1)+(x^2+x+1)]=0
\(\Leftrightarrow\)(x+1)(x^2+x+1)(x^2+1)=0
VÌ x^2+x+1=(x+\(\dfrac{1}{2}\))^2+\(\dfrac{3}{4}\)\(\ne0\) và x^2+1\(\ne0\)
\(\Rightarrow\)x+1=0
\(\Rightarrow\)x=-1
CÒN CÂU B TỰ LÀM (02042006)
b: x^4+3x^3-2x^2+x-3=0
=>x^4-x^3+4x^3-4x^2+2x^2-2x+3x-3=0
=>(x-1)(x^3+4x^2+2x+3)=0
=>x-1=0
=>x=1
(\(x\) - 2)(\(\sqrt{3x+1}\) ) - 1 = 3\(x\) Đk : 3\(x\) + 1 ≥ 0; \(x\) ≥ - \(\dfrac{1}{3}\)
(\(x\) - 2)(\(\sqrt{3x+1}\)) - (3\(x\) + 1) = 0
\(\sqrt{3x+1}\).(\(x\) - 2 - \(\sqrt{3x+1}\)) = 0
\(\left[{}\begin{matrix}\sqrt{3x+1}=0\\x-2-\sqrt{3x+1}\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=-\dfrac{1}{3}\\x-2=\sqrt{3x+1}\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=-\dfrac{1}{3}\\x^2-4x+4=3x+1\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=-\dfrac{1}{3}\\x^2-7x+3=0\end{matrix}\right.\)
\(x^2\) - 7\(x\) + 3 = 0
△ = 49 -12 = 37
\(x_1\) = \(\dfrac{7+\sqrt{37}}{2}\)
\(x_{_{ }2}\) = \(\dfrac{-7-\sqrt{37}}{2}\) (loại)
`(3x-1)(x^2 +2)=(3x-1)(7x-10)`
`<=> (3x-1)(x^2 +2)-(3x-1)(7x-10)=0`
`<=> (3x-1)(x^2 +2-7x+10)=0`
`<=> (3x-1)(x^2 -7x+12)=0`
`<=> (3x-1)(x^2 -3x-4x+12)=0`
`<=> (3x-1)[x(x-3)-4(x-3)]=0`
`<=> (3x-1)(x-4)(x-3)=0`
\(< =>\left[{}\begin{matrix}3x-1=0\\x-4=0\\x-3=0\end{matrix}\right.\\ < =>\left[{}\begin{matrix}x=\dfrac{1}{3}\\x=4\\x=3\end{matrix}\right.\)
\(\left(3x-1\right)\left(x^2+2\right)=\left(3x-1\right)\left(7x-10\right)\)
\(\Leftrightarrow\left(3x-1\right)\left(x^2+2\right)-\left(3x-1\right)\left(7x-10\right)=0\)
\(\Leftrightarrow\left(3x-1\right)\left(x^2+2-7x+10\right)=0\)
\(\Leftrightarrow\left(3x-1\right)\left(x^2-7x+12\right)=0\)
\(\Leftrightarrow\left(3x-1\right)\left(x^2-3x-4x+12\right)=0\)
\(\Leftrightarrow\left(3x-1\right)\left[\left(x^2-3x\right)-\left(4x-12\right)\right]=0\)
\(\Leftrightarrow\left(3x-1\right)\left[x\left(x-3\right)-4\left(x-3\right)\right]=0\)
\(\Leftrightarrow\left(3x-1\right)\left[\left(x-3\right)\left(x-4\right)\right]=0\)
\(\Leftrightarrow\left[{}\begin{matrix}3x-1=0\\x-3=0\\x-4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}3x=1\\x=3\\x=4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{3}\\x=3\\x=4\end{matrix}\right.\)
\(\text{Vậy phương trình có tập nghiệm là }S=\left\{\dfrac{1}{3};3;4\right\}\)
a, đk : x >= 1
\(\left[{}\begin{matrix}3x+5=2x-2\\3x+5=2-2x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-7\\x=-\dfrac{3}{5}\end{matrix}\right.\left(ktm\right)\)
vậy pt vô nghiệm
b, đk >= 0
\(\left[{}\begin{matrix}x^2+1=2x\\x^2+1=-2x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left(x-1\right)^2=0\\\left(x+1\right)^2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\left(tm\right)\\x=-1\left(ktm\right)\end{matrix}\right.\)
c, \(\left[{}\begin{matrix}2x^2+2x=0\\2x^2+4x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x\left(x+1\right)=0\\x^2+2x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0;x=-1\\x=-1\end{matrix}\right.\)
\(\left|2x+1\right|=4.\\ \Leftrightarrow\left[{}\begin{matrix}2x+1=-4.\\2x+1=4.\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{5}{2}.\\x=\dfrac{3}{2}.\end{matrix}\right.\)
\(\left|3x-2\right|+1=0.\)
\(\Leftrightarrow\left|3x-2\right|=-1\) (vô lý).
\(\Rightarrow x\in\phi.\)
Bạn tham khảo thêm ở link sau:
https://hoc24.vn/cau-hoi/giai-phuong-trinhsqrt3x2-5x1-sqrtx2-2sqrt3leftx2-x-1right-sqrtx2-3x4.167769342831
\(\left(3x+1\right)^2=3x+1\)
\(\Leftrightarrow\left(3x+1\right)^2-3x-1=0\)
\(\Leftrightarrow9x^2+6x+1-3x-1=0\)
\(\Leftrightarrow9x^2+3x=0\)
\(\Leftrightarrow3x\left(3x+1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}3x=0\\3x+1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=0\\x=-\frac{1}{3}\end{cases}}}\)
Vậy pt trên có tập nghiệm là \(S=\left(0;-\frac{1}{3}\right)\)
#hok tốt#
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