a: =>7-x=0

hay x=7

b: \(\Leftrightarrow\left(x-\sqrt{2}\right)\left(x+\sqrt{2}\right)\left(x+5\right)\left(3x-8\right)=0\)

hay \(x\in\left\{\sqrt{2};-\sqrt{2};-5;\dfrac{8}{3}\right\}\)

a: =>-x+7=0

hay x=7

b: \(\Leftrightarrow\left(x-\sqrt{2}\right)\left(x+\sqrt{2}\right)\left(x+5\right)\left(3x-8\right)=0\)

hay \(x\in\left\{\sqrt{2};-\sqrt{2};-5;\dfrac{8}{3}\right\}\)

lớp 8 có pt bậc 2 ak??

\(m,x^2+6x-16=0\)

\(\Leftrightarrow x^2-2x+8x-16=0\)

\(\Leftrightarrow x\left(x-2\right)+8\left(x-2\right)=0\)

\(\Leftrightarrow\left(x+8\right)\left(x-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+8=0\\x-2=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-8\\x=2\end{matrix}\right.\)

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

\(\Leftrightarrow2x^2-x+6x-3=0\)

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

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

\(\Leftrightarrow\left[{}\begin{matrix}x+3=0\\2x-1=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=\dfrac{1}{2}\end{matrix}\right.\)

\(k,x\left(2x-7\right)-4x+14=0\)

\(\Leftrightarrow2x^2-4x-7x+14=0\)

\(\Leftrightarrow2x\left(x-2\right)-7\left(x-2\right)=0\)

\(\Leftrightarrow\left(2x-7\right)\left(x-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-7=0\\x-2=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{7}{2}\\x=2\end{matrix}\right.\)

a: \(\Delta=2^2-4\cdot1\cdot\left(-30\right)=124\)

Do đó: Phương trình có hai nghiệm phân biệt là:

\(\left\{{}\begin{matrix}x_1=\dfrac{-2-2\sqrt{31}}{2}=-1-\sqrt{31}\\x_2=-1+\sqrt{31}\end{matrix}\right.\)

b: \(2x^2-3x-5=0\)

\(\Leftrightarrow2x^2-5x+2x-5=0\)

=>(2x-5)(x+1)=0

=>x=5/2 hoặc x=-1

a.\(x^2+2x-30=0\)

\(\Delta=2^2-4.\left(-30\right)=4+120=124>0\)

=> pt có 2 nghiệm

\(\left\{{}\begin{matrix}x=\dfrac{-2+\sqrt{124}}{2}=\dfrac{-2+2\sqrt{31}}{2}=-1+\sqrt{31}\\x=\dfrac{-2-\sqrt{124}}{2}=-1-\sqrt{31}\end{matrix}\right.\)

b.\(2x^2-3x-5=0\)

Ta có: a-b+c=0

\(\Rightarrow\left\{{}\begin{matrix}x=-1\\x=\dfrac{5}{2}\end{matrix}\right.\)( vi-ét )

Ta có: \(\left(x^2-3x+3\right)\left(x^2-2x+3\right)=2x^2\)

\(\Leftrightarrow\left(x^2+3\right)^2-5x\left(x^2+3\right)+6x^2-2x^2=0\)

\(\Leftrightarrow\left(x^2+3\right)^2-5x\left(x^2+3\right)+4x^2=0\)

\(\Leftrightarrow\left(x^2+3\right)^2-x\left(x^2+3\right)-4x\left(x^2+3\right)+4x^2=0\)

\(\Leftrightarrow\left(x^2+3\right)\left(x^2-x+3\right)-4x\left(x^2-x+3\right)=0\)

\(\Leftrightarrow\left(x^2-x+3\right)\left(x^2-4x+3\right)=0\)

mà \(x^2-x+3>0\forall x\)

nên \(x^2-4x+3=0\)

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

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

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

\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=3\end{matrix}\right.\)

Vậy: S={1;3}

Nhận thấy \(x=0\) ko phải nghiệm, pt tương đương:

\(\left(\dfrac{x^2-3x+3}{x}\right)\left(\dfrac{x^2-2x+3}{x}\right)=2\)

\(\Leftrightarrow\left(x+\dfrac{3}{x}-3\right)\left(x+\dfrac{3}{x}-2\right)-2=0\)

Đặt \(x+\dfrac{3}{x}-3=t\)

\(\Rightarrow t\left(t+1\right)-2=0\Leftrightarrow t^2+t-2=0\Rightarrow\left[{}\begin{matrix}t=1\\t=-2\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x^2+\dfrac{3}{x}-3=1\\x^2+\dfrac{3}{x}-3=-2\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x^2-4x+3=0\\x^2-x+3=0\left(vô-nghiệm\right)\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=1\\x=3\end{matrix}\right.\)

1) Ta có: \(x^2-4x+4=0\)

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

\(\Leftrightarrow x-2=0\)

hay x=2

Vậy: S={2}