If x = 0, then y = ?
0 + y = 3
y = 3
we have a sol: (0, 3)
If y = 0, then x = ?
x + 0 = 3
x = 3
we have a sol: (3, 0)
By the points, we have the x-coordinate and the y-coordinate that forms a line that can determine the other solutions that makes the equation true.
