Algebra II : Solving Exponential Equations

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #3 : Solving Exponential Functions

Solve the equation for \displaystyle x.

\displaystyle \small 9^x=3^6

Possible Answers:

\displaystyle \small x=1

\displaystyle \small x=2

\displaystyle \small x=0

\displaystyle \small x=3

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 #12 : Solving Exponential Equations

Solve the equation for \displaystyle x.

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

Possible Answers:

\displaystyle x=1

 

 

 

\displaystyle x=4

\displaystyle x=3

\displaystyle x=9

\displaystyle x=2

 

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 #1 : Solving Exponential Functions

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=1.35(1.0011)^x

\displaystyle y=1034(1.1342)^x

\displaystyle y=1.2(1711)^x

\displaystyle y=1711(1.3932)^x

\displaystyle y=1.1(1034)^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}.

Example Question #1 : Solving Exponential Equations

\displaystyle 4^{5x}=8^{4x-1}

Solve for \displaystyle x.

Possible Answers:

\displaystyle .5

\displaystyle -1

\displaystyle .125

\displaystyle 1

\displaystyle 1.5

Correct answer:

\displaystyle 1.5

Explanation:

8 and 4 are both powers of 2.

\displaystyle 4^{5x}=8^{4x-1}

\displaystyle 2^{10x}=2^{12x-3}

\displaystyle 10x=12x-3 -2x=-3 x=1.5

Example Question #1 : Solving Exponential Functions

Solve for \displaystyle x:

\displaystyle 80^{2x+3}=80^{5x-9}

Possible Answers:

No solution

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

\displaystyle x=4

\displaystyle x=80

\displaystyle x=2

Correct answer:

\displaystyle x=4

Explanation:

Because both sides of the equation have the same base, set the terms equal to each other.

\displaystyle 2x+3=5x-9

Add 9 to both sides: \displaystyle 2x+12=5x

Then, subtract 2x from both sides: \displaystyle 12=3x

Finally, divide both sides by 3: \displaystyle x=4

Example Question #1 : Solving Exponential Equations

Solve for \displaystyle x:

\displaystyle 25^{-x+5}=125^{6x-10}

Possible Answers:

No solution

\displaystyle x=5

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

\displaystyle x=2

\displaystyle x=\frac{15}{7}

Correct answer:

\displaystyle x=2

Explanation:

125 and 25 are both powers of 5.

Therefore, the equation can be rewritten as 

\displaystyle (5^3)^{6x-10}=(5^2)^{-x+5}.

Using the Distributive Property, 

\displaystyle 5^{18x-30}=5^{-2x+10}

Since both sides now have the same base, set the two exponents equal to one another and solve:

\displaystyle 18x-30=-2x+10

Add 30 to both sides: \displaystyle 18x=-2x+40

Add \displaystyle 2x to both sides: \displaystyle 20x=40

Divide both sides by 20: \displaystyle x=2

Example Question #11 : Solving Exponential Functions

Solve \displaystyle 9^{4x+2}=27^{3x-4}.

Possible Answers:

No solution

\displaystyle x=\frac{-16}{9}

\displaystyle x=16

\displaystyle x=6

\displaystyle x=3

Correct answer:

\displaystyle x=16

Explanation:

Both 27 and 9 are powers of 3, therefore the equation can be rewritten as 

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

Using the Distributive Property, 

\displaystyle 3^{8x+4}=3^{9x-12}

Now that both sides have the same base, set the two exponenents equal and solve.

\displaystyle 8x+4=9x-12

Add 12 to both sides: \displaystyle 8x+16=9x

Subtract \displaystyle 8x from both sides: \displaystyle 16=x

Example Question #1 : Solving Exponential Equations

\displaystyle (3)2^{x}=24

Possible Answers:

\displaystyle x=-2

\displaystyle x=4

\displaystyle x=1

\displaystyle x=0

\displaystyle x=3

Correct answer:

\displaystyle x=3

Explanation:

The first step in thist problem is divide both sides by three: \displaystyle 2^{x}=8. Then, recognize that 8 could be rewritten with a base of 2 as well (\displaystyle 2^3). Therefore, your answer is 3.

Example Question #9 : Solving Exponential Equations

Solve for \displaystyle x.

\displaystyle 2^x=64

Possible Answers:

\displaystyle 6

\displaystyle 9

\displaystyle 4

\displaystyle 5

\displaystyle 7

Correct answer:

\displaystyle 6

Explanation:

Let's convert \displaystyle 64 to base \displaystyle 2.

We know the following:

\displaystyle 64=2*2*2*2*2*2

Simplify.

\displaystyle 2*2*2*2*2*2=2^6

Solve.

 \displaystyle x=6

Example Question #10 : Solving Exponential Equations

Solve for \displaystyle x.

\displaystyle 3^x=2187

Possible Answers:

\displaystyle 10

\displaystyle 7

\displaystyle 9

\displaystyle 6

\displaystyle 8

Correct answer:

\displaystyle 7

Explanation:

Let's convert \displaystyle 2187 to base \displaystyle 3.

We know the following:

\displaystyle 2187=3*3*3*3*3*3*3

Simplify.

\displaystyle 3*3*3*3*3*3*3=3^7

Solve.

\displaystyle x=7.

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