College Algebra : Rational Functions

Study concepts, example questions & explanations for College Algebra

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Example Questions

Example Question #1 : Rational Functions

Find all horizontal and vertical asymptotes in the graph of .

Possible Answers:

None of these.

Horizontal asymptote at y=1

Vertical asymptote at x=0

Horizontal asymptote at y=1

Vertical asymptote at x=3

Horizontal asymptote at x=0

Vertical asymptote at y=3

Horizontal asymptote at y=0

Vertical asymptote at x=-3

Correct answer:

Horizontal asymptote at y=1

Vertical asymptote at x=3

Explanation:

To find vertical asymptotes, factor each quadratic and then simplify.

The vertical asymptotes are the zeros of the denominator, so x=3 is a vertical asymptote.

Horizontal asymptotes are found by analyzing the coefficients of the first term in each equation. The line  (where a is the coefficient of the first term in the numerator and b is the coefficient of the first term in the denominator) is the horizontal asymptote. So we have y=1 as the horizontal asymptote.

Example Question #2 : Rational Functions

Where are the vertical asymptotes of this rational function?

Possible Answers:

the function has no vertical asymptotes.

Correct answer:

Explanation:

The vertical asymptotes of a rational function are always the zeroes of the polynomial in the denominator. So to solve this problem all we need to do is find the zeroes of .

We can use the quadratic formula, , for a polynomial . In this case, a=4, b=-8, and c=-5. So we must plug these values into the quadratic formula:

And we get the two roots, .

Example Question #3 : Rational Functions

Which is a vertical asymptote of the graph of the function  ?

(a) 

(b) 

Possible Answers:

(b) only

Both (a) and (b)

Neither (a) nor (b)

(a) only

Correct answer:

(b) only

Explanation:

The vertical asymptote(s) of the graph of a rational function such as  can be found by evaluating the zeroes of the denominator after the rational expression is reduced. The expression is in simplest form, so set the denominator equal to 0 and solve for :

The graph of the line  is the only vertical asymptote of the graph of .

Example Question #4 : Rational Functions

Give the equation(s) of the vertical asymptote(s) of the graph of the function

.

Possible Answers:

 and 

The graph of  has  no vertical asymptotes.

Correct answer:

Explanation:

The vertical asymptote(s) of the graph of a rational function such as  can be found by evaluating the zeroes of the denominator.

Set the denominator equal to 0 and solve for :

The only vertical asymptote of the graph is the line of the equation .

Example Question #2 : Rational Functions

Give the -coordinate of the -intercept the graph of the function 

.

Possible Answers:

The graph of  has no -intercept.

Correct answer:

The graph of  has no -intercept.

Explanation:

The -intercept of the graph of a function is the point at which it intersects the -axis. The -coordinate is 0, so the -coordinate can be found by evaluating . This is done by substitution, as follows:

The value of the denominator here is 0, so  is an undefined quantity. Consequently, the graph of  has no -intercept.

Example Question #6 : Rational Functions

Which is a vertical asymptote of the graph of the function

 ?

(a) 

(b) 

Possible Answers:

(a) only

Both (a) and (b)

Neither (a) nor (b)

(b) only

Correct answer:

(a) only

Explanation:

The vertical asymptote(s) of the graph of a rational function such as  can be found by evaluating the zeroes of the denominator after the rational expression is reduced

First, factor the numerator and denominator.

The numerator is a perfect square trinomial and can be factored as such:

The denominator can be factored as the difference of squares:

Rewrite

as

The expression can be reduced by cancelling  in both halves:

Set the denominator equal to 0 and solve:

The only vertical asymptote is therefore the line of the equation .

Example Question #7 : Rational Functions

Which of the following is a vertical asymptote of the graph of the function  ?

(a) 

(b) 

Possible Answers:

Neither (a) nor (b)

Both (a) and (b)

(a) only

(b) only

Correct answer:

Neither (a) nor (b)

Explanation:

The vertical asymptote(s) of the graph of a rational function such as  can be found by evaluating the zeroes of the denominator after the rational expression is reduced

First, factor the numerator. It is a quadratic trinomial with lead term , so look to "reverse-FOIL" it as

We seek two integers whose sum is  and whose product is ; through trial and error, we find  and 2, so

Therefore,  can be rewritten as 

Cancelling , this can be seen to be essentially a polynomial function:

which does not have a vertical asymptote.

 

Example Question #8 : Rational Functions

Give the -coordinate(s) of the -intercept(s) the graph of the function .

Possible Answers:

The graph of  has no -intercept.

Correct answer:

Explanation:

The -intercept(s) of the graph of  are the point(s) at which it intersects the -axis. The -coordinate of each is 0; their -coordinate(s) are those value(s) of  for which , so set up, and solve for , the equation:

A fraction is equal to 0 if and only if the numerator is equal to 0, so set 

Factor out :

By the Zero Product Property, one of the factors must be equal to 0, so either

or 

in which case

However, setting  in the definition, we see that

, an undefined expression due to the zero denominator. 5 cannot be eliminated similarly. Therefore,  is the only -intercept.

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