Answer:
The slope of the line that contains FG is -1
Explanation:
Given
--- equation of EF
Required
Determine the equation of FG
First, we calculate the slope of EF

Make y the subject

A linear equation has the form:

Where

By comparison:

In square EFGH, EF and FG are perpendicular.
So, the relationship between their slopes is:

Where
--- slope of EF
The equation becomes:

