Question

tìm x biết:

a) \(x(4x^2-1)=0\)

b) \(3(x-1)^2-3x(x-5)-2=0\)

c) \(x^3-x^2-x+1\)

d) \(2x^2 -5x-7=0\)

Answer 1

a) x(4x² - 1) = 0

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

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

b) \(3\left(x-1\right)^2-3x\left(x-5\right)-2=0\)

\(\Rightarrow3x^2-6x+3-3x^2+13=0\\ \Rightarrow13-6x=0\\ \Rightarrow x=\dfrac{13}{6}\)

\(d.2x^2-5x-7=0\\ \Rightarrow2x^2+2x-\left(7x+7\right)=0\\ \Rightarrow2x\left(x+1\right)-7\left(x+1\right)=0\\ \Rightarrow\left(2x-7\right)\left(x+1\right)=0\\ \Rightarrow\left[{}\begin{matrix}2x-7=0\Rightarrow x=\dfrac{7}{2}\\x+1=0\Rightarrow x=-1\end{matrix}\right.\)