\(5x^2-23=0\)

\(\Rightarrow5x^2=23\)

\(\Leftrightarrow x^2=\frac{23}{5}\)

\(\Rightarrow x=\sqrt{4,6}=2,144....\)

đặt \(x^2=t\left(t\ge0\right)\)

Khi đó pt trở thành \(2t^2-5t+6=0\)

=> pt vô nghiệm ! 

_Kudo_

Đặt t = x² (t \(\ge\) 0)

Khi đo ta có pt: 2t² - 5t + 6 = 0

<=> 2(t² - \(\frac{5}{2}\)t + 3) = 0

<=> 2(t² - \(\frac{5}{2}\)t +  \(\frac{25}{16}\) + \(\frac{23}{16}\)) = 0

<=> 2(t - \(\frac{5}{4}\))² + \(\frac{23}{8}\) = 0

<=> 2(t - \(\frac{5}{4}\))² = -\(\frac{23}{8}\)(VN)

Vậy pt vô nghiệm

2x⁴-5x²+6=0

Đặt x² = t(t ≥ 0)

Khi đó pt trở thành 2t² − 5t + 6 = 0

=> pt vô nghiệm ! 

Phân tích đa thức thành nhân tử , ta đươc :

\(x^4+2x^3+5x^2+4x-12=0\)

\(\Leftrightarrow\left(x+2\right)\left(x-1\right)\left(x^2+x+6\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x_1=-2\\x_2=1\end{array}\right.;x^2+x+6=\left(x+\frac{1}{2}\right)^2+5\frac{3}{4}\ne0\forall x.\)

Vậy pt đã cho các nghiệm : \(x_1=-2;x_2=1.\)

2x³-2x²-3x²+3x=0

<=>2x(x-1)-3x(x-1)=0

<=>(x-1)(2x-3x)=0

<=>-x(x-1)=0

Th₁:-x=0

<=>x=0

Th₂:x-1=0

<=>x=1

Vậy phương trình có tập n_o là S=(0, 1)

\(2x^3-5x^2+3x=0\)

\(\Leftrightarrow2x^3-2x^2-3x^2+3x=0\)

\(\Leftrightarrow2x\left(x-1\right)-3x\left(x-1\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(2x-3x\right)=0\)

\(\Leftrightarrow-x\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}-x=0\\\\x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\\\x=1\end{matrix}\right.\)

2x3-2x2-3x2+3x=0

<=>2x(x-1)-3x(x-1)=0

<=>(x-1)(2x-3x)=0

<=>-x(x-1)=0

\(\left\{{}\begin{matrix}-x=0\\x-1=0\end{matrix}\right.\)

\(\left\{{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)

Vậy phương trình có tập no là S=(0, 1)

\(5x-10=0\)
\(5x=10\)
\(x=2\)

5x-10=0

<=>5x=10

<=>x=2

\(5x-10=0\\ 5x=10\\ x=2\)

a) 2x²-4x-x+2=0

=> 2x(x-2)-(x-2)=0

=> (2x-1)(x-2)=0

=> \(\left[{}\begin{matrix}2x-1=0\\x-2=0\end{matrix}\right.\)

=>\(\left[{}\begin{matrix}x=\dfrac{1}{2}\\x=2\end{matrix}\right.\)

b) 3x²-12x+5x-20=0

=> 3x(x-4)+5.(x-4)=0

=> (x-4)(3x+5)=0

=> \(\left[{}\begin{matrix}x-4=0\\3x+5=0\end{matrix}\right.\)

=>\(\left[{}\begin{matrix}x=4\\x=-\dfrac{5}{3}\end{matrix}\right.\)

c)x³+2x²-x²-2x+2x+4=0

=> x²(x+2)-x(x+2)+2(x+2)=0

=>(x²-x+2)(x+2)=0

=> x=-2( vi x²-x+2>0)

d) x³-x²-4x²+4x+4x-4=0

=> x²(x-1)-4x(x-1)+4(x-1)=0

=>(x-1)(x²-4x+4)=0

=> \(\left[{}\begin{matrix}x-1=0\\x^2-4x+4=0\end{matrix}\right.\)

=> \(\left[{}\begin{matrix}x=1\\x=2\end{matrix}\right.\)

2x²-5x+2=0

⇔2x²-x-4x+2=0

⇔x(2x-1)-2(2x-1)=0

⇔(x-2)(2x-1)=0

⇔\(\left[{}\begin{matrix}x-2=0\\2x-1=0\end{matrix}\right.\)⇔\(\left[{}\begin{matrix}x=2\\2x=1\Leftrightarrow x=\dfrac{1}{2}\end{matrix}\right.\)

sậy S=\(\left\{2;\dfrac{1}{2}\right\}\)

x³+x²+4=0

⇔x³+2x²-x²-2x+2x+4=0

⇔(x³+2x²)-(x²+2x)+(2x+4)=0

⇔x²(x+2)-x(x+2)+2(x+2)=0

⇔(x+2)(x²-x+2)=0

⇔x+2=0 và x²-x+2=0

⇔x=-2 và \(\left(x+\dfrac{1}{2}\right)^2+\dfrac{7}{4}=0\)(vô lý)

vậy S={-2}

\(5x^2-4\left(m+1\right)x+2=0\)

Xét \(\Delta'=4\left(m^2+2m+1\right)-10=4m^2+8m-6\)

Nếu \(\Delta'< 0\)=> PT vô nghiệm

Nếu \(\Delta'=0\) thì PT có nghiệm kép \(x_1=x_2=\frac{2\left(m+1\right)}{5}\)

Nếu \(\Delta'>0\)thì PT có 2 nghiệm phân biệt \(\left\{{}\begin{matrix}x_1=\frac{2\left(m+1\right)-\sqrt{4m^2+8m-6}}{10}\\x_2=\frac{2\left(m+1\right)+\sqrt{4m^2+8m-6}}{10}\end{matrix}\right.\)