GRE Math : How to find the slope of a perpendicular line

Study concepts, example questions & explanations for GRE Math

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Example Questions

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Example Question #1 : How To Find The Slope Of A Perpendicular Line

A line is defined by the following equation:

What is the slope of a line that is perpendicular to the line above?

Possible Answers:

Correct answer:

Explanation:

The equation of a line is  where  is the slope.

Rearrange the equation to match this:

For the perpendicular line, the slope is the negative reciprocal;

therefore 

Example Question #91 : Coordinate Geometry

The equation of a particular line is as follows: 

.  

What is the slope of a line perpendicuar to this one?

Possible Answers:

Correct answer:

Explanation:

The slope of a perpendicular line is the opposite reciporical of the originial slope.  

The opposite would be changing the sign from positive to negative or vice versa.  

The reciporical is flipping the fraction or switching the numerator and denominator.  

This equation is in slope-intercept form,

meaning m represents the slope of the equation.

Since the original is  , then the perpendicular would be positive and would swtich the 7 and 3 giving us .

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