point-slope form with perpendicular line

Question

can you explain how to get this answer?  a line passes throught *8,-1) and is perpendicular to y=2x-9.  What is the equation of the line in point-slope form?

Answer 1

Perpendicular lines have slopes that are opposite reciprocals. So if the line need to be perpendicular to y = 2x - 9, the slope would need to be -1/2. Since it also has to go through (8, -1), use the slope and the point to write the equation in point-slope form.