Perpendicular lines have opposite reciprocal slopes.
x = 4 has a slope of undefined since it is a vertical line.
It's undefined because 1/0 = undefined. We can't divide by 0.
The opposite reciprical of 1/0 is -0/1, which equals to 0.
Any line with a slope of 0 is:
y = 0x + b
y = b
This line goes through the point of (3, 5).
Since the equation starts with y = something, we have to use the y-value of the point it goes through. The point is in the form of (x, y).
5 is in the y-value.
The equation of the perpendicular line is y = 5.