Algebra II : Solving and Graphing Radicals

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #81 : Solving Radical Equations

Solve the equation:  \(\displaystyle \sqrt[3]{-6x-9} = 4\)

Possible Answers:

\(\displaystyle -\frac{73}{6}\)

\(\displaystyle -\frac{73}{3}\)

\(\displaystyle -\frac{13}{6}\)

\(\displaystyle -\frac{65}{6}\)

\(\displaystyle -\frac{7}{3}\)

Correct answer:

\(\displaystyle -\frac{73}{6}\)

Explanation:

Raise both sides by the power of three in order to eliminate the radical.

\(\displaystyle (\sqrt[3]{-6x-9} )^3= 4^3\)

\(\displaystyle -6x-9 =64\)

Add nine on both sides.

\(\displaystyle -6x-9 +9=64+9\)

\(\displaystyle -6x =73\)

Divide by negative six on both sides.

\(\displaystyle \frac{-6x}{-6} =\frac{73}{-6}\)

The answer is:  \(\displaystyle -\frac{73}{6}\)

Example Question #82 : Solving Radical Equations

Solve:  \(\displaystyle \sqrt[3]{3x-6} = \frac{1}{2}\)

Possible Answers:

\(\displaystyle \frac{37}{18}\)

\(\displaystyle \frac{49}{24}\)

\(\displaystyle -\frac{35}{18}\)

\(\displaystyle -\frac{47}{24}\)

\(\displaystyle -\frac{49}{24}\)

Correct answer:

\(\displaystyle \frac{49}{24}\)

Explanation:

Cube both sides to eliminate the radical.

\(\displaystyle (\sqrt[3]{3x-6} )^3= (\frac{1}{2})^3\)

The equation becomes:  \(\displaystyle 3x-6 = \frac{1}{8}\)

Multiply by eight on both sides to eliminate the fraction.

\(\displaystyle 8(3x-6)= \frac{1}{8}\cdot 8\)

\(\displaystyle 24x-48=1\)

Add 48 on both sides.

\(\displaystyle 24x-48+48=1+48\)

\(\displaystyle 24x=49\)

Divide by 24 on both sides.

\(\displaystyle \frac{24x}{24}=\frac{49}{24}\)

The answer is:  \(\displaystyle \frac{49}{24}\)

Example Question #83 : Solving Radical Equations

Solve:  \(\displaystyle \sqrt{9x}+2 = 16\)

Possible Answers:

\(\displaystyle \frac{196}{9}\)

\(\displaystyle \frac{9}{49}\)

\(\displaystyle 36\)

\(\displaystyle \frac{62}{3}\)

\(\displaystyle \frac{1}{7}\)

Correct answer:

\(\displaystyle \frac{196}{9}\)

Explanation:

Subtract two from both sides.

\(\displaystyle \sqrt{9x}+2 -2= 16-2\)

\(\displaystyle \sqrt{9x} = 14\)

Square both sides in order to eliminate the radical.

\(\displaystyle (\sqrt{9x}) ^2= 14^2\)

\(\displaystyle 9x=196\)

Divide by nine on both sides.

\(\displaystyle \frac{9x}{9}=\frac{196}{9}\)

The right side is irreducible.

The answer is:  \(\displaystyle \frac{196}{9}\)

Example Question #84 : Solving Radical Equations

Solve the radical:  \(\displaystyle \sqrt{-5x+3} = 3\)

Possible Answers:

\(\displaystyle -\frac{6}{5}\)

\(\displaystyle 0\)

\(\displaystyle -\frac{1}{5}\)

\(\displaystyle -\frac{45}{4}\)

\(\displaystyle -\frac{5}{6}\)

Correct answer:

\(\displaystyle -\frac{6}{5}\)

Explanation:

Square both sides in order to eliminate the radical.

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

The equation becomes:

\(\displaystyle -5x+3=9\)

Subtract three from both sides.

\(\displaystyle -5x+3-3=9-3\)

\(\displaystyle -5x=6\)

Divide by negative five on both sides.

\(\displaystyle \frac{-5x}{-5}=\frac{6}{-5}\)

The answer is:  \(\displaystyle -\frac{6}{5}\)

Example Question #401 : Radicals

Solve:  \(\displaystyle \sqrt[5]{-3x}-3 = -1\)

Possible Answers:

\(\displaystyle -\frac{20}{3}\)

\(\displaystyle \textup{No solution.}\)

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

\(\displaystyle -\frac{16}{3}\)

\(\displaystyle -\frac{32}{3}\)

Correct answer:

\(\displaystyle -\frac{32}{3}\)

Explanation:

Add three on both sides.

\(\displaystyle \sqrt[5]{-3x}-3+3 = -1+3\)

\(\displaystyle \sqrt[5]{-3x} = 2\)

Raise both sides by the power of five to eliminate the radical.

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

\(\displaystyle -3x =32\)

Divide by negative three on both sides.

\(\displaystyle \frac{-3x }{-3}=\frac{32}{-3}\)

The answer is:  \(\displaystyle -\frac{32}{3}\)

Example Question #402 : Radicals

Solve the equation:  \(\displaystyle \sqrt5 \cdot \sqrt{2x} -10= -9\)

Possible Answers:

\(\displaystyle \textup{No solution.}\)

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

\(\displaystyle \frac{1}{10}\)

\(\displaystyle \frac{1}{20}\)

\(\displaystyle \frac{1}{5}\)

Correct answer:

\(\displaystyle \frac{1}{10}\)

Explanation:

The radicals can be combined as one radical by multiplying the two inner terms together.

The equation becomes:

\(\displaystyle \sqrt{10x} -10= -9\)

Add 10 on both sides.

\(\displaystyle \sqrt{10x} -10+10= -9+10\)

Simplify both sides.

\(\displaystyle \sqrt{10x} =1\)

Square both sides.

\(\displaystyle 10x=1\)

Divide by ten on both sides.

\(\displaystyle \frac{10x}{10}=\frac{1}{10}\)

The answer is:  \(\displaystyle \frac{1}{10}\)

Example Question #403 : Radicals

Solve the radical:  \(\displaystyle \sqrt{\sqrt{2x}} = \sqrt{8}\)

Possible Answers:

\(\displaystyle 128\)

\(\displaystyle 16\)

\(\displaystyle 64\)

\(\displaystyle 32\)

\(\displaystyle 256\)

Correct answer:

\(\displaystyle 32\)

Explanation:

Rewrite the radicals so that they are in exponential form.

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

\(\displaystyle \sqrt{\sqrt{2x}} =[ (2x)^{\frac{1}{2}}]^{\frac{1}{2}} = (2x)^{\frac{1}{4}}\)

The equation becomes:

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

Raise both sides by the power of four to eliminate the fractional exponents.

\(\displaystyle [(2x)^{\frac{1}{4}}] ^4= [8^{\frac{1}{2}}]^4\)

\(\displaystyle 2x=64\)

Divide by two on both sides.

\(\displaystyle \frac{2x}{2}=\frac{64}{2}\)

The answer is:  \(\displaystyle 32\)

Example Question #404 : Radicals

Solve:  \(\displaystyle 4=2^{10x-8}\)

Possible Answers:

\(\displaystyle \frac{3}{4}\)

\(\displaystyle -4\)

\(\displaystyle 1\)

\(\displaystyle -1\)

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

Correct answer:

\(\displaystyle 1\)

Explanation:

Evaluate by changing the base of the left term.

\(\displaystyle 2^2=2^{10x-8}\)

Now that both bases are common, set the powers equal and solve for x.

\(\displaystyle 2=10x-8\)

Add 8 on both sides.

\(\displaystyle 2+8=10x-8+8\)

\(\displaystyle 10=10x\)

Divide by ten on both sides.

\(\displaystyle \frac{10}{10}=\frac{10x}{10}\)

The answer is:  \(\displaystyle 1\)

Example Question #405 : Radicals

Evaluate:  \(\displaystyle \sqrt[3]{2x-8} = 2\)

Possible Answers:

\(\displaystyle \textup{No solution.}\)

\(\displaystyle 16\)

\(\displaystyle -8,8\)

\(\displaystyle 4\)

\(\displaystyle 8\)

Correct answer:

\(\displaystyle 8\)

Explanation:

Cube both sides to eliminate the radical.

\(\displaystyle (\sqrt[3]{2x-8}) ^3= 2^3\)

\(\displaystyle 2x-8 =8\)

Add eight on both sides.

\(\displaystyle 2x-8+(8) =8+(8)\)

\(\displaystyle 2x=16\)

Divide by 2 on both sides.

\(\displaystyle \frac{2x}{2}=\frac{16}{2}\)

The answer is:  \(\displaystyle 8\)

Example Question #406 : Radicals

Solve:  \(\displaystyle 2\sqrt[3]{2-5x} = 10\)

Possible Answers:

\(\displaystyle \frac{13}{5}\)

\(\displaystyle -\frac{123}{5}\)

\(\displaystyle \frac{123}{5}\)

\(\displaystyle \frac{127}{5}\)

\(\displaystyle -\frac{13}{5}\)

Correct answer:

\(\displaystyle -\frac{123}{5}\)

Explanation:

Solve by first dividing both sides by two.

\(\displaystyle \frac{2\sqrt[3]{2-5x} }{2}= \frac{10}{2}\)

Simplify both sides.

\(\displaystyle \sqrt[3]{2-5x} =5\)

Cube both sides.

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

\(\displaystyle 2-5x =125\)

Subtract two from both sides.

\(\displaystyle 2-5x -(2)=125-(2)\)

\(\displaystyle -5x=123\)

Divide by negative five on both sides.

\(\displaystyle \frac{-5x}{-5}=\frac{123}{-5}\)

The answer is:  \(\displaystyle -\frac{123}{5}\)

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