In the xy – plane, what is the slope of line perpendicular

In the xy – plane, what is the slope of line perpendicular to line K?

You should know 2 important things:

1. For one line to be perpendicular to another, the relationship between their slopes has to be negative reciprocal, so if the slope of one line is \(m\) then the line prependicular to it will have the slope \(-\frac{1}{m}\). In other words, the two lines are perpendicular if and only the product of their slopes is -1.

2. Parallel lines have the same slope.

(1) line K intersects line with equation 2x + 3y = 4 at point Q (2,0) --> clearly insufficient, as we don't know the angle at which the line K intersects this line (we just have some line and know that K intersect it at some point). Not sufficient.

(2) Line K does not intersect line with equation y = 2x-5 --> K is parallel to this line so has the same slope --> slope of K=2 --> the line perpendicular to line K will have the slope -1/2. Sufficient.

Answer: B.

For more on these issues check Coordinate Geometry chapter of Math Book: math-coordinate-geometry-87652.html

Hope it helps.