The slope of a line that is perpendicular to a line whose slope is 3/8 is:

Ans:-8/3

The product of the gradients of two lines that are perpendicular to each other is -1

The equation of the line through point (- 4, 0) and parallel to the y-axis is

Ans:x = -4

Question repeated

In the figure, M and N are midpoints of RT and ST. What is the length of MN?

Ans: b - a

Midpoint of a line:

A square has symmetry with respect to a line containing a median of the square.

Forgive my ignorance please. What's the median of a square?