Question 1 of 5
In the -plane, line passes through the points and . A second line passes through the origin and is perpendicular to line . Which of the following is the equation of a line through the point that is parallel to line ?
Explanation
First find the slope of line using its two points:
A line perpendicular to line has slope equal to the negative reciprocal of , which is . Since line is perpendicular to line , line has slope . Any line parallel to line also has slope . So the desired line through has equation
Substitute the point :
Thus,
The equation is
which is choice B.
Concept summary
Find a line's slope from two points, use the negative reciprocal to get a perpendicular slope, and use point-slope or slope-intercept form to write an equation through a given point.