College Algebra : Exponential and Logarithmic Functions

Study concepts, example questions & explanations for College Algebra

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Example Questions

Example Question #1 : Exponential And Logarithmic Functions

Solve:  

Possible Answers:

The answer does not exist.

\displaystyle 2x

\displaystyle 2

\displaystyle \frac{1}{2x+3}

\displaystyle 2x+3

Correct answer:

\displaystyle 2x+3

Explanation:

To solve , it is necessary to know the property of \displaystyle e.  

Since \displaystyle e and the \displaystyle ln terms cancel due to inverse operations, the answer is what's left of the \displaystyle ln term.

The answer is:  \displaystyle 2x+3

Example Question #2 : Exponential And Logarithmic Functions

Which equation is equivalent to:

\displaystyle \log _{4}\left( \frac{1}{2}\right)=x

Possible Answers:

\displaystyle (4)^{x}=\left(\frac{1}{2}\right)^{x}

\displaystyle \frac{1^{4}}{2}=x^{4}

\displaystyle 4^{\frac{1}{2}}=x

\displaystyle 4^{x}=\frac{1}{2}

\displaystyle \left(\frac{1}{2}\right)^{4}=x

Correct answer:

\displaystyle 4^{x}=\frac{1}{2}

Explanation:

 

\displaystyle log{_{a}}^{b}=x\displaystyle b>0

\displaystyle \Rightarrow a^{x}=b

So, \displaystyle {{log_{4}}^{\frac{1}{2}}}=x\Rightarrow 4^{x}=\frac{1}{2}

Example Question #2 : Exponential And Logarithmic Functions

\displaystyle Log_{b}x=y

What is the inverse of the log function?

Possible Answers:

\displaystyle b=x\cdot y

\displaystyle b^{x}=y

\displaystyle b^{y}=x

\displaystyle y^{b}=x

\displaystyle x^{b}=y

Correct answer:

\displaystyle b^{y}=x

Explanation:

This is a general formula that you should memorize. The inverse of \displaystyle Log_{b}x=y is \displaystyle b^{y}=x. You can use this formula to change an equation from a log function to an exponential function.

Example Question #3 : Exponential And Logarithmic Functions

Rewrite the following expression as an exponential expression:

\displaystyle log_3b=14,000

Possible Answers:

\displaystyle 3^{14,000}=b

\displaystyle b^{14,000}=3

\displaystyle b^3=14,000

\displaystyle 14,000^3=b

Correct answer:

\displaystyle 3^{14,000}=b

Explanation:

Rewrite the following expression as an exponential expression:

\displaystyle log_3b=14,000

Recall the following property of logs and exponents:

\displaystyle log_b(a)=c 

Can be rewritten in the following form:

\displaystyle b^c=a

So, taking the log we are given;

\displaystyle log_3b=14,000

We can rewrite it in the form:

\displaystyle 3^{14,000}=b

So b must be a really huge number!

Example Question #2 : College Algebra

Convert the following logarithmic equation to an exponential equation:

\displaystyle log_{13}b=147

Possible Answers:

\displaystyle b^{13}=147

\displaystyle 13^{147}=b

\displaystyle 147^b=13

\displaystyle 13^{b}=147

Correct answer:

\displaystyle 13^{147}=b

Explanation:

Convert the following logarithmic equation to an exponential equation:

\displaystyle log_{13}b=147

Recall the following:

This

\displaystyle log_b(a)=c

Can be rewritten as

\displaystyle b^c=a

So, our given logarithm

\displaystyle log_{13}b=147

Can be rewritten as

\displaystyle 13^{147}=b

Fortunately we don't need to expand, because this woud be a very large number!

Example Question #1 : College Algebra

Convert the following logarithmic equation to an exponential equation.

\displaystyle log_3(14x)=156

Possible Answers:

\displaystyle 3^{14x}=156

\displaystyle (14x)^{156}=3

\displaystyle 3^{156}=14x

\displaystyle 156=(14x)^3

Correct answer:

\displaystyle 3^{156}=14x

Explanation:

Convert the following logarithmic equation to an exponential equation.

\displaystyle log_3(14x)=156

To convert from logarithms to exponents, recall the following property:

\displaystyle log_b(x)=a

Can be rewritten as:

\displaystyle b^a=x

So, starting with

\displaystyle log_3(14x)=156,

We can get

\displaystyle 3^{156}=14x

Example Question #3 : College Algebra

Solve the following:

\displaystyle 5^x=125

Possible Answers:

\displaystyle 625

\displaystyle 5

\displaystyle 2

\displaystyle 3

Correct answer:

\displaystyle 3

Explanation:

To solve the following, you must "undo" the 5 with taking log based 5 of both sides. Thus,

\displaystyle 5^x=125

\displaystyle \log_5{5^x}=\log_5{125}

\displaystyle x=\log_5{125}

The right hand side can be simplified further, as 125 is a power of 5. Thus,

\displaystyle x=\log_5{125}

\displaystyle x=\log_5{5^3}

\displaystyle x=3

Example Question #4 : Exponential Functions

Solve for \displaystyle x:

\displaystyle 2^{x}+ 2 ^{x+2} = 171

(Nearest hundredth)

Possible Answers:

\displaystyle x \approx 3.65

\displaystyle x \approx 2.84

The equation has no solution.

\displaystyle x \approx 2.71

\displaystyle x \approx 5.10

Correct answer:

\displaystyle x \approx 5.10

Explanation:

Apply the Product of Powers Property to rewrite the second expression:

\displaystyle 2^{x}+ 2 ^{x+2} = 171

\displaystyle 2^{x}+ 2 ^{2} \cdot 2 ^{x} = 171

\displaystyle 1 \cdot 2^{x}+ 4 \cdot 2 ^{x} = 171

Distribute out: 

\displaystyle (1 + 4) \cdot 2 ^{x} = 171

\displaystyle 5 \cdot 2 ^{x} = 171

Divide both sides by 5:

\displaystyle \frac{5 \cdot 2 ^{x}}{5} = \frac{171}{5}

\displaystyle 2 ^{x} = 34.2

Take the natural logarithm of both sides (and note that you can use common logarithms as well):

\displaystyle \ln 2 ^{x} = \ln 34.2

Apply a property of logarithms:

\displaystyle x \ln 2 = \ln 34.2

Divide by \displaystyle \ln 2 and evaluate:

\displaystyle \frac{x \ln 2}{\ln2} = \frac{\ln 34.2}{\ln2}

\displaystyle x = \frac{3.5322 }{0.6931 }

\displaystyle x \approx 5.10

Example Question #4 : Exponential And Logarithmic Functions

Solve for \displaystyle x:

\displaystyle 3^{2x+ 1} = 9^{2x- 4 }

(Nearest hundredth, if applicable).

Possible Answers:

The equation has no solution.

\displaystyle x= 3.25

\displaystyle x = 4.50

\displaystyle x= 1.10

\displaystyle x = 3.40

Correct answer:

\displaystyle x = 4.50

Explanation:

\displaystyle 9 = 3^{2}, so rewrite the expression at right as a power of 3 using the Power of a Power Property:

\displaystyle 3^{2x+ 1} = 9^{2x- 4 }

\displaystyle 3^{2x+ 1} = (3^{2} )^{2x- 4 }

\displaystyle 3^{2x+ 1} = 3^{2(2x- 4 )}

Set the exponents equal to each other and solve the resulting linear equation:

\displaystyle 2x+ 1 = 2(2x-4)

Distribute:

\displaystyle 2x+ 1 = 4x-8

Subtract \displaystyle 4x and 1 from both sides; we can do this simultaneously:

\displaystyle 2x+ 1 - 4x - 1 = 4x-8 - 4x - 1

\displaystyle - 2x = -9

Divide by \displaystyle -2:

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

\displaystyle x =4.5

Example Question #1 : College Algebra

Solve the following for x:

\displaystyle \log(2x+4)=1

Possible Answers:

\displaystyle 48

\displaystyle 7

\displaystyle \frac{-3}{2}

\displaystyle 3

Correct answer:

\displaystyle 3

Explanation:

To solve, you must first "undo" the log. Since no base is specified, you assume it is 10. Thus, we need to take 10 to both sides.

\displaystyle 10^{\log(2x+4)}=10^1

\displaystyle 2x+4=10

Now, simply solve for x.

\displaystyle 2x=6

\displaystyle x=3

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