Question

(x- căn 2)+3(x²-2)

Answer 1

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

cái \(1+3\sqrt{2}\) là tính ra một số vô tỉ nên tớ để vậy luôn