Algebra II : Mathematical Relationships and Basic Graphs

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #9 : Natural Log

Determine the value of:  \(\displaystyle 2e\cdot ln(e^3)\)

Possible Answers:

\(\displaystyle 6e^5\)

\(\displaystyle 5e\)

\(\displaystyle 6e\)

\(\displaystyle e^6\)

\(\displaystyle e^7\)

Correct answer:

\(\displaystyle 6e\)

Explanation:

In order to simplify this expression, use the following natural log rule.

\(\displaystyle ln_x(x^y) =y\)

The natural log has a default base of \(\displaystyle e\). This means that: 

 \(\displaystyle 2e\cdot ln(e^3)=2e\cdot ln_e(e^3) = 2e\cdot (3)\)

The answer is:  \(\displaystyle 6e\)

Example Question #4 : Natural Log

Simplify:  \(\displaystyle 2e^{4ln{(2e)}}\)

Possible Answers:

\(\displaystyle 32e^4\)

\(\displaystyle 32e^2\)

\(\displaystyle 64e^4\)

\(\displaystyle 16e\)

\(\displaystyle 16e^4\)

Correct answer:

\(\displaystyle 32e^4\)

Explanation:

According to log properties, the coefficient \(\displaystyle 4\) in front of the natural log can be rewritten as the exponent raised by the quantity inside the log.

\(\displaystyle 2e^{4ln{(2e)}} = 2e^{ln[{(2e)^4}]}\)

Notice that natural log has a base of \(\displaystyle e\).  This means that raising the log by base \(\displaystyle e\) will eliminate both the \(\displaystyle e\) and the natural log.

The terms become:  \(\displaystyle 2(2e)^4\)

Simplify the power.

\(\displaystyle 2(2e)^4 = 2(16e^4) = 32e^4\)

The answer is:  \(\displaystyle 32e^4\)

Example Question #11 : Natural Log

Evaluate:  \(\displaystyle 2e^2ln(e^2)\)

Possible Answers:

\(\displaystyle 4e^4\)

\(\displaystyle 4e^2\)

\(\displaystyle 8e\)

\(\displaystyle 4\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 4e^2\)

Explanation:

The natural log has a default base of \(\displaystyle e\).  Natural log to of an exponential raised to the power will be just the power.  The natural log and \(\displaystyle e\) will be eliminated.

\(\displaystyle ln(e^x)=x\)

Rewrite the expression.

\(\displaystyle 2e^2ln(e^2) = 2e^2(2) = 4e^2\)

The answer is:  \(\displaystyle 4e^2\)

Example Question #11 : Logarithms

Determine the value of:  \(\displaystyle 6ln(e^{-3x})\)

Possible Answers:

\(\displaystyle -216x\)

\(\displaystyle -3x+6\)

\(\displaystyle -9x\)

\(\displaystyle -18x\)

\(\displaystyle -\frac{1}{2}x\)

Correct answer:

\(\displaystyle -18x\)

Explanation:

The natural log has a default base of \(\displaystyle e\).  

According to the rule of logs, we can use:

\(\displaystyle log_{b}(b^x) = x\)

\(\displaystyle 6ln(e^{-3x}) = 6ln_e(e^{-3x})\)

The coefficient in front of the natural log can be transferred as the power of the exponent.

\(\displaystyle 6ln_e(e^{-3x}) = ln_e(e^{(-3x)(6)})\)

The natural log and base e will cancel, leaving just the exponent.

\(\displaystyle (-3x)(6)=-18x\)

The answer is:  \(\displaystyle -18x\)

Example Question #12 : Natural Log

Solve:  \(\displaystyle 3ln(e^{7e})\)

Possible Answers:

\(\displaystyle 21e\)

\(\displaystyle 7e^3\)

\(\displaystyle 21e^2\)

\(\displaystyle 21\)

\(\displaystyle 7e^2\)

Correct answer:

\(\displaystyle 21e\)

Explanation:

The natural log has a default base of \(\displaystyle e\).  This means that the natural log of \(\displaystyle e\) to the certain power will be just the power itself.

\(\displaystyle log_{b}(b^x) = x\)

The expression \(\displaystyle 3ln(e^{7e})\) becomes:  

\(\displaystyle 3(7e) = 21e\)

The answer is:  \(\displaystyle 21e\)

Example Question #11 : Natural Log

Simplify:  \(\displaystyle ln(6e^7)\)

Possible Answers:

\(\displaystyle ln(2)+ln(3)+7\)

\(\displaystyle ln(42e)\)

\(\displaystyle 42e\)

\(\displaystyle 42\)

\(\displaystyle ln(5)+e^7\)

Correct answer:

\(\displaystyle ln(2)+ln(3)+7\)

Explanation:

Use the log properties to separate each term.  When the terms inside are multiplied, the logs can be added.

Rewrite the expression.

\(\displaystyle ln(6e^7) = ln(6)+ln(e^7) = ln(2)+ln(3)+ln(e^7)\)

The exponent, 7 can be dropped as the coefficient in front of the natural log.  Natural log of the exponential is equal to one since the natural log has a default base of \(\displaystyle e\).

\(\displaystyle log_{b}(b^x) = x\)

The answer is:  \(\displaystyle ln(2)+ln(3)+7\)

Example Question #15 : Natural Log

The equation  \(\displaystyle kt = ln(\frac{T-S}{T_0-S})\) represents Newton's Law of Cooling.  Solve for \(\displaystyle T_0\).

Possible Answers:

\(\displaystyle T_0 =\frac{e^{kt}S-T}{e^{kt}+S}\)

\(\displaystyle T_0 =\frac{T-S+e^{kt}S}{e^{kt}}\)

\(\displaystyle T_0 =\frac{T+e^{kt}S}{e^{kt}+S}\)

\(\displaystyle T_0 =\frac{T-e^{kt}S}{e^{kt}+S}\)

\(\displaystyle T_0 =\frac{e^{kt}S}{e^{kt}+S+T}\)

Correct answer:

\(\displaystyle T_0 =\frac{T-S+e^{kt}S}{e^{kt}}\)

Explanation:

Use base \(\displaystyle e\) and raise both the left and right sides as the powers of \(\displaystyle e\).  This will eliminate the natural log term.

\(\displaystyle e^{kt} =e^ {ln(\frac{T-S}{T_0-S})}\)

The equation becomes:

\(\displaystyle e^{kt} =\frac{T-S}{T_0-S}\)

Multiply the quantity \(\displaystyle (T_0-S)\) on both sides.

\(\displaystyle e^{kt}(T_0-S) =\frac{T-S}{T_0-S}(T_0-S)\)

\(\displaystyle e^{kt}T_0-e^{kt}S =T-S\)

Add \(\displaystyle e^{kt}S\) on both sides.

\(\displaystyle e^{kt}T_0-e^{kt}S +e^{kt}S=T-S+e^{kt}S\)

The equation becomes:

\(\displaystyle e^{kt}T_0=T-S+e^{kt}S\)

To isolate \(\displaystyle T_0\), divide \(\displaystyle e^{kt}\) on both sides.

\(\displaystyle \frac{e^{kt}T_0}{e^{kt}}=\frac{T-S+e^{kt}S}{e^{kt}}\)

The answer is:  \(\displaystyle T_0 =\frac{T-S+e^{kt}S}{e^{kt}}\)

Example Question #16 : Natural Log

Evaluate:  \(\displaystyle 2e^2ln(e^{2e})\)

Possible Answers:

\(\displaystyle 4e\)

\(\displaystyle 2e^2+2e\)

\(\displaystyle e+4\)

\(\displaystyle 4e^2+e\)

\(\displaystyle 4e^3\)

Correct answer:

\(\displaystyle 4e^3\)

Explanation:

The natural log has a default base of \(\displaystyle e\).

Use the log property:

\(\displaystyle log_x(x^y)=y\)

We can cancel the base and the log of the base.

The expression \(\displaystyle 2e^2ln(e^{2e})\) becomes:

\(\displaystyle 2e^2(2e )= 4e^3\)

The answer is:  \(\displaystyle 4e^3\)

Example Question #11 : Understanding Logarithms

Simplify:  \(\displaystyle ln(e+e^2)\)

Possible Answers:

\(\displaystyle 2\)

\(\displaystyle 3\)

\(\displaystyle 1+ln(e+1)\)

\(\displaystyle 1\)

\(\displaystyle 2e+1\)

Correct answer:

\(\displaystyle 1+ln(e+1)\)

Explanation:

Notice that the terms inside the log are added, with a common factor of \(\displaystyle e\).  Pull out a common factor.

\(\displaystyle ln(e+e^2)= ln((e)(1+e))\)

Notice that these two terms inside the log are multiplied.  We can split the log into two terms.

\(\displaystyle ln((e)(1+e)) = ln(e)+ln(e+1)\)

The value of the first term is equal to one, since natural log has a default base of \(\displaystyle e\).  We can use the property \(\displaystyle ln_xx^y=y\) to eliminate the log and the \(\displaystyle e\) term, which will cancel leaving just the power of one.

The expression becomes:  \(\displaystyle 1+ln(e+1)\)

We cannot use the property of logs to simplify the second term.

The answer is:  \(\displaystyle 1+ln(e+1)\)

Example Question #18 : Natural Log

Solve the expression:  \(\displaystyle ln(2x+e)= 13\)

Possible Answers:

\(\displaystyle \frac{e^{13}-e}{2}\)

\(\displaystyle \frac{e^{13}+e}{2}\)

\(\displaystyle \frac{e^{12}}{2}\)

\(\displaystyle \frac{e^6}{2}\)

\(\displaystyle \frac{13-e}{2e}\)

Correct answer:

\(\displaystyle \frac{e^{13}-e}{2}\)

Explanation:

In order to eliminate the natural log and solve for x, we will need to exponential both sides because \(\displaystyle e\) is the base of natural log.

\(\displaystyle e^{ln(2x+e)}= e^{13}\)

The left side will be reduced to just the inner quantity of the natural log.

\(\displaystyle 2x+e = e^{13}\)

Subtract \(\displaystyle e\) from both sides of the equation.

\(\displaystyle 2x+e -e= e^{13}-e\)

\(\displaystyle 2x= e^{13}-e\)

Divide by two on both sides.

\(\displaystyle \frac{2x}{2}= \frac{e^{13}-e}{2}\)

The answer is:  \(\displaystyle \frac{e^{13}-e}{2}\)

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