Question

Bài 1: Tìm x biết

2x ( x-3) -5 (3-x) = 0
Bài 2: Tìm GTNN của: B= x^2 + 4x+5
Bài 6: Thực hiện phép chia:
(2x^3-5x^2-x+1):(2x+1)

Answer 1

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

\(\Leftrightarrow2x\left(x-3\right)+5\left(x-3\right)=0\)

\(\Leftrightarrow\left(2x+5\right)\left(x-3\right)=0\)

\(\Rightarrow\left\{{}\begin{matrix}2x+5=0\\x-3=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=-\dfrac{5}{2}\\x=3\end{matrix}\right.\)

2.\(B=x^2+4x+5\)

\(B=x^2+4x+4+1\)

\(B=\left(x+2\right)^2+1\)

Vì \(\left(x+2\right)^2\ge0\forall x\)

\(\Rightarrow\left(x+2\right)^2+1\ge1\)

\(\Rightarrow Min_B=1\) khi x+2=0\(\Rightarrow\)x=-2

Answer 2

bài 6:

\(=\dfrac{2x^3+x^2-6x^2-3x+2x+1}{2x+1}=x^2-3x+1\)