Algebra II : Solving and Graphing Exponential Equations

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #1 : Solving Functions

What is the horizontal asymptote of the graph of the equation \displaystyle y = -2e^{x-3} -5 ?

Possible Answers:

\displaystyle y=-\frac{5}{2}

\displaystyle y=-2

\displaystyle y=5

\displaystyle y=-5

\displaystyle y=3

Correct answer:

\displaystyle y=-5

Explanation:

The asymptote of this equation can be found by observing that \displaystyle e^{x-3} > 0 regardless of \displaystyle x. We are thus solving for the value of \displaystyle y as \displaystyle e^{x-3} approaches zero.

\displaystyle -2e^{x-3} < -2\cdot 0

\displaystyle -2e^{x-3} < 0

\displaystyle -2e^{x-3} -5 < 0-5

\displaystyle -2e^{x-3} -5 < -5

\displaystyle y< -5

So the value that \displaystyle y cannot exceed is \displaystyle -5, and the line \displaystyle y = -5 is the asymptote.

Example Question #1 : Solving Functions

What is/are the asymptote(s) of the graph of the function

\displaystyle f(x) = 5e^{x-2}-2 ?

Possible Answers:

\displaystyle y = -2, x=2 

\displaystyle y = -2, x=-2

\displaystyle x=2

\displaystyle y = -2

\displaystyle x=-2

Correct answer:

\displaystyle y = -2

Explanation:

An exponential equation of the form \displaystyle f(x) = ae^{x-h} +k has only one asymptote - a horizontal one at \displaystyle y = k. In the given function, \displaystyle k = -2, so its one and only asymptote is \displaystyle y = -2.

 

 

Example Question #341 : Sat Subject Test In Math I

Find the vertical asymptote of the equation.

\displaystyle y=\frac{x^2-9}{x^2-16}

Possible Answers:

\displaystyle x=4

\displaystyle x=1

\displaystyle x=0

There are no vertical asymptotes.

\displaystyle x=4, -4

Correct answer:

\displaystyle x=4, -4

Explanation:

To find the vertical asymptotes, we set the denominator of the function equal to zero and solve.

\displaystyle 0=x^2-16

\displaystyle 16=x^2

\displaystyle \sqrt{16}=\sqrt{x^2}

\displaystyle 4, -4=x

Example Question #1 : Solving And Graphing Exponential Equations

Determine the asymptotes, if any:  \displaystyle y=\frac{x^2-2x+1}{x^2-1}

Possible Answers:

\displaystyle x=\pm1

\displaystyle x=1

\displaystyle \textup{There are no asymptotes.}

\displaystyle x=-\frac{1}{2}

\displaystyle x=-1

Correct answer:

\displaystyle x=-1

Explanation:

Factorize both the numerator and denominator.

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

Notice that one of the binomials will cancel.

The domain of this equation cannot include \displaystyle x=\pm1.

The simplified equation is:

\displaystyle y=\frac{x-1}{x+1}

Since the \displaystyle (x-1) term canceled, the \displaystyle (x-1) term will have a hole instead of an asymptote.   

Set the denominator equal to zero.

\displaystyle x+1=0

Subtract one from both sides.

\displaystyle x=-1

There will be an asymptote at only:  \displaystyle x=-1

The answer is:  \displaystyle x=-1

Example Question #2 : Find The Equations Of Vertical Asymptotes Of Tangent, Cosecant, Secant, And Cotangent Functions

Which of the choices represents asymptote(s), if any?   \displaystyle y=\frac{2x^2+2x}{x^2-8x-9}

Possible Answers:

\displaystyle x=9

\displaystyle x=9\textup{ and }y=\frac{2}{5}

\displaystyle \textup{There are no asymptotes.}

\displaystyle x=1, 9\textup{ and } y= -\frac{2}{5}

\displaystyle x=1, 9

Correct answer:

\displaystyle x=9

Explanation:

Factor the numerator and denominator.

\displaystyle y=\frac{2x^2+2x}{x^2-8x-9} = \frac{2x(x+1)}{(x-9)(x+1)}

Notice that the \displaystyle (x+1) terms will cancel.  The hole will be located at \displaystyle x=-1 because this is a removable discontinuity.

\displaystyle y=\frac{2x}{x-9}

The denominator cannot be equal to zero.  Set the denominator to find the location where the x-variable cannot exist.

\displaystyle x-9\neq0

\displaystyle x\neq9

The asymptote is located at \displaystyle x=9.

Example Question #2 : Solving And Graphing Exponential Equations

Where is an asymptote located, if any?   \displaystyle y=\frac{2x-4}{x^2-4}

Possible Answers:

\displaystyle y=-2

\displaystyle y=2

\displaystyle x=2

\displaystyle \textup{There is no asymptote.}

\displaystyle x=-2

Correct answer:

\displaystyle x=-2

Explanation:

Factor the numerator and denominator.

\displaystyle 2x-4 = 2(x-2)

\displaystyle x^2-4 = (x+2)(x-2)

Rewrite the equation.

\displaystyle y=\frac{2x-4}{x^2-4}=\frac{ 2(x-2)}{(x+2)(x-2)}=\frac{2}{x+2}

Notice that the \displaystyle (x-2) will cancel.  This means that the root of \displaystyle (x-2) will be a hole instead of an asymptote.

Set the denominator equal to zero and solve for x.

\displaystyle x+2=0

\displaystyle x=-2

An asymptote is located at:  \displaystyle x=-2

The answer is:  \displaystyle x=-2

Example Question #2 : Solving Exponential Functions

Consider the exponential function \displaystyle y=2^x+3. Determine if there are any asymptotes and where they lie on the graph.

Possible Answers:

There is one vertical asymptote at \displaystyle y=3.

There is one horizontal asymptote at \displaystyle y=3.

There is one vertical asymptote at \displaystyle y=2.

There are no asymptotes. \displaystyle y goes to positive infinity in both the \displaystyle +x and \displaystyle -x directions.

Correct answer:

There is one horizontal asymptote at \displaystyle y=3.

Explanation:

For positive \displaystyle x values, \displaystyle y increases exponentially in the \displaystyle +x direction and goes to positive infinity, so there is no asymptote on the positive \displaystyle x-axis. For negative \displaystyle x values, as \displaystyle x decreases, the term \displaystyle 2^x becomes closer and closer to zero so \displaystyle y approaches \displaystyle 3 as we move along the negative \displaystyle x axis. As the graph below shows, this is forms a horizontal asymptote.

Exp_asymp

Example Question #641 : Exponents

Solve the equation for \displaystyle x.

\displaystyle \small 9^x=3^6

Possible Answers:

\displaystyle \small x=3

\displaystyle \small x=2

\displaystyle \small x=1

\displaystyle \small x=0

Correct answer:

\displaystyle \small x=3

Explanation:

Begin by recognizing that both sides of the equation have a root term of \displaystyle 3.

\displaystyle \small 9^x=3^6

\displaystyle (3^2)^x=3^6

Using the power rule, we can set the exponents equal to each other.

\displaystyle 3^{(2*x)}=3^6

\displaystyle \small 2x=6

\displaystyle \small x=3

Example Question #51 : Functions And Graphs

Solve the equation for \displaystyle x.

\displaystyle \small 3^{2x}=81

Possible Answers:

\displaystyle x=4

\displaystyle x=2

 

\displaystyle x=3

\displaystyle x=1

 

 

 

\displaystyle x=9

Correct answer:

\displaystyle x=2

 

Explanation:

Begin by recognizing that both sides of the equation have the same root term, \displaystyle 3.

\displaystyle \small 3^{2x}=81

\displaystyle \small 3^{2x}=9^2

\displaystyle 3^{2x}=(3^2)^2

We can use the power rule to combine exponents.

\displaystyle 3^{2x}=3^4

Set the exponents equal to each other.

\displaystyle 2x=4

\displaystyle \small x=2

Example Question #3 : Solving And Graphing Exponential Equations

In 2009, the population of fish in a pond was 1,034. In 2013, it was 1,711.

Write an exponential growth function of the form \displaystyle y=ab^{x}} that could be used to model \displaystyle y, the population of fish, in terms of \displaystyle x, the number of years since 2009.

Possible Answers:

\displaystyle y=1711(1.3932)^x

\displaystyle y=1034(1.1342)^x

\displaystyle y=1.1(1034)^x

\displaystyle y=1.2(1711)^x

\displaystyle y=1.35(1.0011)^x

Correct answer:

\displaystyle y=1034(1.1342)^x

Explanation:

Solve for the values of and b:

In 2009, \displaystyle y=1034 and \displaystyle x=0 (zero years since 2009). Plug this into the exponential equation form:

\displaystyle 1034=ab^{(0)}. Solve for \displaystyle a to get  \displaystyle a=1034.

In 2013, \displaystyle y=1711 and \displaystyle x=4. Therefore,

\displaystyle 1711=ab^4  or  \displaystyle 1711=(1034)b^4.   Solve for \displaystyle b to get

\displaystyle b=\sqrt[4]{\frac{1711}{1034}}\approx1.1342.

Then the exponential growth function is  

\displaystyle y=1034(1.1342)^{x}.

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