Given the information on the coordinate plane, we can see that the points A and B are (-2,-2) and (2,-2) respectively. Then, to find the slope we have:
[tex]\begin{gathered} m=\frac{y_2-y_1}{x_2-x_1} \\ \Rightarrow m=\frac{-2-(-2)}{2-(-2)}=\frac{-2+2}{2+2}=\frac{0}{4}=0 \\ m=0 \end{gathered}[/tex]
We have that the slope is 0, and to find the equation, we can use the equation y=mx+b to find out, using either points A or B:
[tex]\begin{gathered} y=mx+b \\ (x,y)=(-2,-2) \\ m=0 \\ \Rightarrow-2=0\cdot(-2)+b \\ \Rightarrow-2=b \end{gathered}[/tex]
Therefore, the equation of the diagonal AB is y=-2
