Question

What is the slope and y-intercept of the line `x=-6`?

Answer 1

The line is vertical.
It does not have a y-intercept at all.
The gradient is undefined (infinite).
This vertical line does not cross the `y-` axis anywhere.

Explanation:

`x = -6` is a vertical line crossing the x-axis at -6.
It does not cross the y-axis at all, so there is no y-intercept.

Lines which are vertical are said to have an infinite or undefined gradient.
The definition of gradient is `("change in y-values")/("change in x-values")`

As there is no change in the x-values the denominator would be 0.
Vertical lines are only ones which cannot be written in the standard form of `y = mx + c` and are always given as `x = .....`