a)Q(x)=2x2+3x
Cho Q(x)=0
<=>2x2+3x=0
<=>x(2x+3)=0
<=>x=0 hoặc 2x+3=0
<=>x=0 hoặc x=-\(\dfrac{3}{2}\)
Vậy...
b)Cho x2+4x+5=0
<=>(x2+4x+4)+1=0
<=>(x+2)2+1=0(1)
Do (x+2)2\(\ge\)0 với mọi x
=>(x+2)2+1\(\ge\)1>0 với mọi x
=>(1) vô nghiệm
Vậy...
a)\(\left\{{}\begin{matrix}Q\left(x\right)=2x^2+3x\\Q\left(x\right)=0\end{matrix}\right.\)\(\Rightarrow2x^2+3x=0\)
\(\Rightarrow x\left(2x+3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\2x+3=0\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=0\\x=-\dfrac{3}{2}\end{matrix}\right.\)
b)\(x^2+4x+5=x^2+4x+4+1=\left(x+2\right)^2+1\ge1>0\forall x\)
Vô nghiệm
