2:
a: 
b: Tọa độ A là:
\(\left\{{}\begin{matrix}y=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-1\\y=0\end{matrix}\right.\)
=>A(-1;0)
tọa độ B là:
\(\left\{{}\begin{matrix}y=0\\3-x=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=0\\x=3\end{matrix}\right.\)
=>B(3;0)
Tọa độ C là:
\(\left\{{}\begin{matrix}x+1=-x+3\\y=x+1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x=2\\y=x+1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=2\end{matrix}\right.\)
=>C(1;2)
c: A(-1;0); B(3;0); C(1;2)
\(AB=\sqrt{\left(3+1\right)^2+\left(0-0\right)^2}=4\)
\(AC=\sqrt{\left(1+1\right)^2+2^2}=2\sqrt{2}\)
\(BC=\sqrt{\left(1-3\right)^2+2^2}=2\sqrt{2}\)
\(C_{ABC}=2\sqrt{2}+2\sqrt{2}+4=4\sqrt{2}+4\)
\(BC^2+AC^2=AB^2\)
=>ΔABC vuông tại C
=>\(S_{CAB}=\dfrac{1}{2}\cdot CA\cdot CB=\dfrac{1}{2}\cdot2\sqrt{2}\cdot2\sqrt{2}=4\)