Question

(x+3)(x²-3x+5)=x²+3x

Answer 1

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

\(\Rightarrow\left(x+3\right)\left(x^2-3x+5\right)=x\left(x+3\right)\)

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

\(\Rightarrow x=-3\)(do \(x^2-4x+5=\left(x-2\right)^2+1\ge1>0\))

Answer 2

\(\Rightarrow\left(x+3\right)\left(x^2-3x+5\right)-x\left(x+3\right)=0\\ \Rightarrow\left(x+3\right)\left(x^2-4x+5\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=-3\\\left(x-2\right)^2+1=0\left(vô.lí\right)\end{matrix}\right.\Rightarrow x=-3\)