Question

A line passes through (1,2) and is perpendicular to y=3.

Answer 1

Make a graph and put a point at exactly (1,2) and then make a like at y=3 make a line through the point and you'll see that this is an undefined equation x cant equal all those numbers

Answer 2

As the line is perpendicular to y = 3  it well be of the form x = some number.
And the point (1,2)  has an x-coordinate of 1   so the line passes through x = 1.

Equation of the required line is x = 1. Answer