Question

How would I find a line perpendicular to: `y=2x+5`?

Answer 1

Perpendicular lines have gradients whose product is `-1`.

Straight lines in standard form `y=mx+c` has gradient m and y-intercept c.

So `y=2x+5` has gradient `2`.

So any line of gradient `-1/2` will be perpendicular to this line,
ie. any line of form `y=-1/2x+c`