Normally, lines are parallel if their slopes are identical and perpendicular if their slopes are negative reciprocals. However, the given lines are kind of special.
y=& -7
x=& 2
Given an equation in the form y=b, for any point (x,y) on the graph we know that no matter the value of x, the y value will always be b. Such a line runs parallel to the x-axis. This is, by definition, a horizontal line.
Similarly, for the graph of an equation in the form x=a, the x value of any point (x,y) on the graph will always equal a, regardless of the value of y. Such a line runs parallel to the y-axis. This is, by definition, a vertical line.
Just as the x-axis and y-axis are perpendicular to one another, any lines parallel to the x-axis are perpendicular to any lines parallel to the y-axis. Therefore, y=-7 is perpendicular to x=2.
