Question

tìm x, biết :

(3-x)(x²+1)=0

Answer 1

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

\(\Rightarrow x=3\)(do \(x^2+1\ge1>0\forall x\))

Answer 2

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

Vậy \(x=3\)

Answer 3

Vì `x^2  >=0\ forall x -> x^2+1 >= 1 >0 `

` -> 3-x=0`

`-> x=3`.

Answer 4

Ta có: \(x^2+1>0dox^2\ge0\) với mọi x.

Khi đó: \(3-x=0\Rightarrow x=3\)

Answer 5

vô lí