SAT II Math II : Solving Exponential, Logarithmic, and Radical Functions

Study concepts, example questions & explanations for SAT II Math II

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Example Questions

Example Question #1 : Solving Exponential, Logarithmic, And Radical Functions

Rewrite as a single logarithmic expression:

\(\displaystyle \ln (y+ 1) - \ln (y + 2) + \ln (y + 3)\)

Possible Answers:

\(\displaystyle = \ln \frac{y^{2}+4y + 3}{y + 2}\)

\(\displaystyle \ln \left (y + 4 \right )\)

\(\displaystyle \ln \frac{y^{2}+3}{y + 2}\)

\(\displaystyle \ln \left (y + 2 \right )\)

\(\displaystyle = \ln \frac{y+1}{y^{2}+5y+6}\)

Correct answer:

\(\displaystyle = \ln \frac{y^{2}+4y + 3}{y + 2}\)

Explanation:

Using the properties of logarithms

\(\displaystyle \ln a - \ln b = \ln \frac{a}{b}\) and \(\displaystyle \ln a + \ln b = \ln ab\),

simplify as follows:

\(\displaystyle \ln (y+ 1) - \ln (y + 2) + \ln (y + 3)\)

\(\displaystyle = \ln \frac{y+ 1}{y + 2} + \ln (y + 3)\)

\(\displaystyle = \ln \left [\frac{y+ 1}{y + 2} \cdot (y + 3) \right ]\)

\(\displaystyle = \ln \frac{y^{2}+4y + 3}{y + 2}\)

Example Question #1 : Solving Exponential, Logarithmic, And Radical Functions

Simplify by rationalizing the denominator:

\(\displaystyle \frac{11}{6- \sqrt{3}}\)

Possible Answers:

\(\displaystyle \frac{6- \sqrt{3}}{3 }\)

\(\displaystyle \frac{6+ \sqrt{3}}{3 }\)

\(\displaystyle 2- \sqrt{3}\)

\(\displaystyle 2+ \sqrt{3}\)

\(\displaystyle \frac{11\sqrt{3}}{3}\)

Correct answer:

\(\displaystyle \frac{6+ \sqrt{3}}{3 }\)

Explanation:

Multiply the numerator and the denominator by the conjugate of the denominator, which is \(\displaystyle 6 + \sqrt{3}\). Then take advantage of the distributive properties and the difference of squares pattern:

\(\displaystyle \frac{11}{6- \sqrt{3}}\)

\(\displaystyle = \frac{11(6+ \sqrt{3})}{\left (6- \sqrt{3} \right )(6+ \sqrt{3})}\)

\(\displaystyle = \frac{11(6+ \sqrt{3})}{ 6^{2}- \left (\sqrt{3} \right ) ^{2}\right }\)

\(\displaystyle = \frac{11(6+ \sqrt{3})}{36-3 }\)

\(\displaystyle = \frac{11(6+ \sqrt{3})}{3 3 }\)

\(\displaystyle = \frac{6+ \sqrt{3}}{3 }\)

 

Example Question #3 : Solving Functions

Simplify:

\(\displaystyle \sqrt[3]{\sqrt[2]{x^{-9}}}\)

You may assume that \(\displaystyle x\) is a nonnegative real number.

Possible Answers:

\(\displaystyle \frac{ \sqrt[3]{x}}{x }\)

\(\displaystyle \frac{1}{x^{3}}\)

\(\displaystyle \frac{ \sqrt{x}}{x^{2}}\)

\(\displaystyle \sqrt[3]{x}\)

\(\displaystyle x \sqrt{x}\)

Correct answer:

\(\displaystyle \frac{ \sqrt{x}}{x^{2}}\)

Explanation:

The best way to simplify a radical within a radical is to rewrite each root as a fractional exponent, then convert back.

First, rewrite the roots as exponents.

\(\displaystyle \sqrt[3]{\sqrt[2]{x^{-9}}} = \sqrt[3]{\left ( x^{-9} \right ) ^{\frac{1}{2}} } = \left ( \left ( x^{-9} \right ) ^{\frac{1}{2}} \right )^{\frac{1}{3}} = x ^{-9 \cdot \frac{1}{2} \cdot \frac{1}{3}} } } = x ^{- \frac{3}{2} } }= \frac{1}{x^{\frac{3}{2}}}\)

Then convert back to a radical and rationalizing the denominator:

\(\displaystyle \frac{1}{x^{\frac{3}{2}}} = \frac{1}{\sqrt {x^{3}}} = \frac{1 \cdot \sqrt{x}}{\sqrt {x^{3} \cdot \sqrt{x}}} = \frac{ \sqrt{x}}{\sqrt {x^{4} }} =\frac{ \sqrt{x}}{x^{2}}\)

Example Question #1 : Solving Exponential, Logarithmic, And Radical Functions

Let \(\displaystyle f(x) = 2^{x}+ 3^{2x}\).   What is the value of \(\displaystyle f(-2)\)?

Possible Answers:

\(\displaystyle \frac{85}{324}\)

\(\displaystyle \frac{1}{85}\)

\(\displaystyle -85\)

\(\displaystyle \textup{The answer is not given.}\)

\(\displaystyle 85\)

Correct answer:

\(\displaystyle \frac{85}{324}\)

Explanation:

Replace the integer as \(\displaystyle x\).

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

Evaluate each negative exponent.

\(\displaystyle 2^{-2} = \frac{1}{2^2} = \frac{1}{4}\)

\(\displaystyle 3^{-4} = \frac{1}{3^4} = \frac{1}{81}\)

Sum the fractions.

\(\displaystyle \frac{1}{4}+\frac{1}{81} = \frac{1(81)}{4(81)}+\frac{1(4)}{81(4)} = \frac{85}{324}\)

The answer is:  \(\displaystyle \frac{85}{324}\)

Example Question #1 : Solving Exponential, Logarithmic, And Radical Functions

Find \(\displaystyle x\):   \(\displaystyle \sqrt{-3x-5} = 7\)

Possible Answers:

\(\displaystyle -54\)

\(\displaystyle -18\)

\(\displaystyle -4\)

\(\displaystyle -9\)

\(\displaystyle 18\)

Correct answer:

\(\displaystyle -18\)

Explanation:

Square both sides to eliminate the radical.

\(\displaystyle (\sqrt{-3x-5}) ^2= 7^2\)

\(\displaystyle -3x-5 = 49\)

Add five on both sides.

\(\displaystyle -3x-5 +5= 49+5\)

\(\displaystyle -3x = 54\)

Divide by negative three on both sides.

\(\displaystyle \frac{-3x}{-3} = \frac{54}{-3}\)

The answer is:  \(\displaystyle -18\)

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