1: Thay x=0 và y=4 vào (d), ta được:
\(0\left(m^2+1\right)+m+2=4\)
=>m+2=4
=>m=2
2: tọa độ A là:
\(\left\{{}\begin{matrix}y=0\\x\left(m^2+1\right)+m+2=0\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=\dfrac{-m-2}{m^2+1}\\y=0\end{matrix}\right.\)
Tọa độ B là: \(\left\{{}\begin{matrix}x=0\\y=0\left(m^2+1\right)+m+2=m+2\end{matrix}\right.\)
vậy: O(0;0); \(A\left(\dfrac{-m-2}{m^2+1};0\right);B\left(0;m+2\right)\)
\(OA=\sqrt{\left(\dfrac{-m-2}{m^2+1}-0\right)^2+\left(0-0\right)^2}=\sqrt{\dfrac{\left(m+2\right)}{m^2+1}}^2=\dfrac{\left|m+2\right|}{m^2+1}\)
\(OB=\sqrt{\left(0-0\right)^2+\left(m+2-0\right)^2}=\sqrt{0^2+\left(m+2\right)^2}=\left|m+2\right|\)
Vì Ox\(\perp\)Oy nên ΔOAB vuông tại O
=>\(S_{OAB}=\dfrac{1}{2}\cdot OA\cdot OB=\dfrac{1}{2}\cdot\dfrac{\left(m+2\right)^2}{m^2+1}\)
Để \(S_{OBA}=\dfrac{1}{2}\) thì \(\dfrac{1}{2}\cdot\dfrac{\left(m+2\right)^2}{m^2+1}=\dfrac{1}{2}\)
=>\(\dfrac{\left(m+2\right)^2}{m^2+1}=1\)
=>\(\left(m+2\right)^2=m^2+1\)
=>\(m^2+4m+4=m^2+1\)
=>4m+4=1
=>4m=-3
=>\(m=-\dfrac{3}{4}\)
