We can use y = mx + b to show the line at x = 0 is y = b:
y = m*0 + b
y = b
From this we might see that the line x = 0 in a line on the y-axis.
We can also use the slope m = y/x for the line x = 0:
m = y/0
m = ∞
From this we see Infinite slope that is a vertical line. A vertical line at x = 0 is a line on the y-axis.
For a perpendicular line to an infinite slope we can take the negative reciprocal m = -x/y:
m = -0/y
m = 0
For the point given (3, 1) we can use y - y1 = m*( x - x1) with m = 0:
y - 1 = 0*( x - 3)
y = 1 (the answer)
