Precalculus : Polynomial Functions

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Find A Point Of Discontinuity

Find a point of discontinuity for the following function:

\displaystyle s(x)=\frac{180-5x^2}{x^2-36}

Possible Answers:

\displaystyle (-5, -6)

\displaystyle (-6, -5)

\displaystyle (6, 5)

There are no points of discontinuity for this function.

Correct answer:

\displaystyle (-6, -5)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle s(x)=\frac{180-5x^2}{x^2-36}=\frac{-5(x^2-36)}{(x-6)(x+6)}=\frac{-5(x-6)(x+6)}{(x-6)(x+6)}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=\pm 6 is a zero for both the numerator and denominator, there is a point of discontinuity there. Since the final function is \displaystyle s(x)=-5\displaystyle (6, -5) and \displaystyle (-6, -5) are points of discontinuity.

Example Question #8 : Find A Point Of Discontinuity

Find a point of discontinuity in the following function:

\displaystyle f(x)=\frac{x^2+x-12}{x^2+2x-8}

Possible Answers:

There is no point of discontinuity for this function.

\displaystyle (0, 4)

\displaystyle \left(-2, \frac{5}{7}\right)

\displaystyle \left(-4, \frac{7}{6}\right)

Correct answer:

\displaystyle \left(-4, \frac{7}{6}\right)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle f(x)=\frac{x^2+x-12}{x^2+2x-8}=\frac{(x+4)(x-3)}{(x+4)(x-2)}=\frac{(x-3)}{(x-2)}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=-4 is a zero for both the numerator and denominator, there is a point of discontinuity there. To find the \displaystyle y value, plug in \displaystyle -4 into the final simplified equation.

\displaystyle \frac{-4-3}{-4-2}=\frac{7}{6}

\displaystyle \left(-4, \frac{7}{6}\right) is the point of discontinuity.

 

Example Question #9 : Find A Point Of Discontinuity

Find the point of discontinuity for the following function:

\displaystyle g(x)=\frac{x^2-1}{x^2+8x+7}

Possible Answers:

\displaystyle \left(1, \frac{1}{3}\right)

There is no point of discontinuity.

\displaystyle \left(-1, -\frac{1}{3}\right)

\displaystyle (2, 4)

Correct answer:

\displaystyle \left(-1, -\frac{1}{3}\right)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle g(x)=\frac{x^2-1}{x^2+8x+7}=\frac{(x-1)(x+1)}{(x+1)(x+7)}=\frac{x-1}{x+7}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=-1 is a zero for both the numerator and denominator, there is a point of discontinuity there. To find the \displaystyle y value, plug in \displaystyle -1 into the final simplified equation.

\displaystyle \frac{-1-1}{-1+7}=-\frac{1}{3}

\displaystyle \left(-1, -\frac{1}{3}\right) is the point of discontinuity.

 

Example Question #1 : Find A Point Of Discontinuity

Find the point of discontinuity for the following function:

\displaystyle h(x)=\frac{x^2-5x+6}{x^2-9}

Possible Answers:

There is no point of discontinuity for this function.

\displaystyle \left(6, -\frac{2}{3}\right)

\displaystyle \left(5, \frac{1}{8}\right)

\displaystyle \left(3, \frac{1}{6}\right)

Correct answer:

\displaystyle \left(3, \frac{1}{6}\right)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle h(x)=\frac{x^2-5x+6}{x^2-9}=\frac{(x-2)(x-3)}{(x-3)(x+3)}=\frac{x-2}{x+3}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=3 is a zero for both the numerator and denominator, there is a point of discontinuity there. To find the \displaystyle y value, plug in \displaystyle 3 into the final simplified equation.

\displaystyle \frac{3-2}{3+3}=\frac{1}{6}

\displaystyle \left(3, \frac{1}{6}\right) is the point of discontinuity.

 

Example Question #21 : Rational Functions

Find the point of discontinuity for the following function:

\displaystyle j(x)=\frac{x^2+7x+6}{x^2-1}

Possible Answers:

\displaystyle \left(1, \frac{5}{2}\right)

There is no point of discontinuity for this function.

\displaystyle (-3, 6)

\displaystyle \left(-1, -\frac{5}{2}\right)

Correct answer:

\displaystyle \left(-1, -\frac{5}{2}\right)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle j(x)=\frac{x^2+7x+6}{x^2-1}=\frac{(x+6)(x+1)}{(x+1)(x-1)}=\frac{x+6}{x-1}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=-1 is a zero for both the numerator and denominator, there is a point of discontinuity there. To find the \displaystyle y value, plug in \displaystyle -1 into the final simplified equation.

\displaystyle \frac{-1+6}{-1-1}=-\frac{5}{2}

\displaystyle \left(-1, -\frac{5}{2}\right) is the point of discontinuity.

 

Example Question #11 : Find A Point Of Discontinuity

Find the point of discontinuity for the following function:

\displaystyle k(x)=\frac{2x^2-x-1}{x^2-6x+5}

Possible Answers:

\displaystyle \left(1, -\frac{3}{4}\right)

\displaystyle \left(-5, \frac{9}{10}\right)

There is no point of discontinuity for this function.

\displaystyle (1, 4)

Correct answer:

\displaystyle \left(1, -\frac{3}{4}\right)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle k(x)=\frac{2x^2-x-1}{x^2-6x+5}=\frac{(2x+1)(x-1)}{(x-1)(x-5)}=\frac{2x+1}{x-5}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=1 is a zero for both the numerator and denominator, there is a point of discontinuity there. To find the \displaystyle y value, plug in \displaystyle 1 into the final simplified equation.

\displaystyle \frac{2(1)+1}{1-5}=-\frac{3}{4}

\displaystyle \left(1, -\frac{3}{4}\right) is the point of discontinuity.

 

Example Question #11 : Find A Point Of Discontinuity

Find the point of discontinuity for the following function:

\displaystyle l(x)=\frac{2x^2+5x-12}{x^2+3x-4}

Possible Answers:

\displaystyle (-3, 0)

\displaystyle (4, 1)

There is no point of discontinuity for this function.

\displaystyle \left(-4, \frac{11}{5}\right)

Correct answer:

\displaystyle \left(-4, \frac{11}{5}\right)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle l(x)=\frac{2x^2+5x-12}{x^2+3x-4}=\frac{(2x-3)(x+4)}{(x+4)(x-1)}=\frac{2x-3}{x-1}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=-4 is a zero for both the numerator and denominator, there is a point of discontinuity there. To find the \displaystyle y value, plug in \displaystyle -4 into the final simplified equation.

\displaystyle \frac{2(-4)-3}{-4-1}=\frac{11}{5}

\displaystyle \left(-4, \frac{11}{5}\right) is the point of discontinuity.

 

Example Question #12 : Find A Point Of Discontinuity

Find the point of discontinuity for the following function:

\displaystyle n(x)=\frac{x^3+2x^2-3x}{x^2+8x+15}

Possible Answers:

\displaystyle (-3, 6)

There is no point of discontinuity for this function.

\displaystyle (-4, 20)

\displaystyle \left(-1, \frac{1}{2}\right)

Correct answer:

\displaystyle (-3, 6)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle n(x)=\frac{x^3+2x^2-3x}{x^2+8x+15}=\frac{x(x^2+2x-3)}{(x+3)(x+5)}=\frac{x(x-1)(x+3)}{(x+3)(x+5)}=\frac{x(x-1)}{x+5}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=-3 is a zero for both the numerator and denominator, there is a point of discontinuity there. To find the \displaystyle y value, plug in \displaystyle -3 into the final simplified equation.

\displaystyle \frac{-3(-3-1)}{-3+5}=6

\displaystyle (-3, 6) is the point of discontinuity.

 

Example Question #12 : Find A Point Of Discontinuity

Find the point of discontinuity for the following function:

\displaystyle q(x)=\frac{x^2+x}{x^3+3x^2-x-3}

Possible Answers:

\displaystyle \left(-1, \frac{1}{4}\right)

\displaystyle (-3, 2)

\displaystyle (0, 4)

There is no discontinuity for this function.

Correct answer:

\displaystyle \left(-1, \frac{1}{4}\right)

Explanation:

Start by factoring the numerator and denominator of the function.

\displaystyle q(x)=\frac{x^2+x}{x^3+3x^2-x-3}=\frac{x(x+1)}{(3x^2-3)(x^3-x)}

\displaystyle =\frac{x(x+1)}{3(x^2-1)x(x^2-1)}=\frac{x(x+1)}{(x-1)(x+1)(x+3)}=\frac{x}{(x-1)(x+3)}

A point of discontinuity occurs when a number \displaystyle a is both a zero of the numerator and denominator.

Since \displaystyle x=-1 is a zero for both the numerator and denominator, there is a point of discontinuity there. To find the \displaystyle y value, plug in \displaystyle -1 into the final simplified equation.

\displaystyle \frac{-1}{(-1-1)(-1+3)}=\frac{1}{4}

\displaystyle \left(-1, \frac{1}{4}\right) is the point of discontinuity.

Example Question #11 : Find A Point Of Discontinuity

Given the function, \displaystyle y=\frac{8x-4}{4x-2}, where and what is the type of discontinuity, if any?  

Possible Answers:

Correct answer:

Explanation:

Before we simplify, set the denominator equal to zero to determine where \displaystyle x is invalid.  The value of the denominator cannot equal to zero.

\displaystyle 4x-2 \neq0

\displaystyle 4x \neq2

\displaystyle x\neq \frac{2}{4} \neq \frac{1}{2}

The value at \displaystyle x=\frac{1}{2} is invalid in the domain.

Pull out a greatest common factor for the numerator and the denominator and simplify.

\displaystyle y=\frac{8x-4}{4x-2} =\frac{4(2x-1)}{2(2x-1)} = 2

Since the terms \displaystyle 2x-1 can be cancelled, there will not be any vertical asymptotes.  Even though the rational function simplifies to \displaystyle y=2, there will be instead a hole at \displaystyle x=\frac{1}{2} on the graph.  

The answer is:  

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