Solve the Exponential Equation: x^14 - x^7 = 0

Exponential Equations with Common Factoring

Solve the following problem:

x14x7=0 x^{14}-x^7=0

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find X
00:03 Factor with X to the power of 7
00:11 Take out the common factor from the parentheses
00:22 This is one solution that zeros the equation
00:26 Now let's check which solutions zero the second factor
00:30 Isolate X
00:34 1 to an odd root is always equal to 1
00:38 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the following problem:

x14x7=0 x^{14}-x^7=0

2

Step-by-step solution

Shown below is the given equation:

x14x7=0 x^{14}-x^7=0

Note that on the left side we are able factor the expression by using a common factor. The largest common factor for the numbers and letters in this case is x7 x^{7} given that the seventh power is the lowest power in the equation. Therefore it is included both in the term with the 14th power and in the term with the seventh power. Any power higher than this is not included in the term with the lowest seventh power. Hence this is the term with the highest power that can be factored out as a common factor from all terms for the letters,

Let's continue to factor the equation:

x14x7=0x7(x71)=0 x^{14}-x^7=0 \\ \downarrow\\ x^{7}(x^7-1)=0

Proceed to the left side of the equation that we obtained in the last step. There is a multiplication of algebraic expressions and on the right side the number 0. Therefore due to the fact that the only way to obtain 0 from a multiplication is to multiply by 0, at least one of the expressions in the multiplication on the left side must equal zero,

Meaning:

x7=0/7x=0 x^{7}=0 \hspace{8pt}\text{/}\sqrt[7]{\hspace{6pt}}\\ \boxed{x=0}

In solving the above equation, we extracted a 99th root for both sides of the equation.

(In this case, extracting an odd-order root to the right side of the equation yielded one possibility)

Or:

x71=0x7=1/7x=1 x^7-1=0\\ x^7=1\hspace{8pt}\text{/}\sqrt[7]{\hspace{6pt}}\\ \boxed{x=1}

In solving the above equation, we first isolated the variable (because it's possible..) on one side and then extracted a seventh root for both sides of the equation.

(In this case, again, extracting an odd-order root to the right side of the equation yielded one possibility)

Let's summarize the solution of the equation:

x14x7=0x7(x71)=0x7=0x=0x71=0x=1x=0,1 x^{14}-x^7=0 \\ \downarrow\\ x^{7}(x^7-1)=0 \\ \downarrow\\ x^{7}=0 \rightarrow\boxed{ x=0}\\ x^{7}-1=0\rightarrow \boxed{x=1}\\ \downarrow\\ \boxed{x=0,1}

Therefore the correct answer is answer D.

3

Final Answer

Answers a + b

Key Points to Remember

Essential concepts to master this topic
  • Factoring Rule: Extract highest common power from all terms first
  • Technique: Factor out x7 x^7 to get x7(x71)=0 x^7(x^7-1) = 0
  • Check: Substitute both solutions: 01407=0 0^{14} - 0^7 = 0 and 11417=0 1^{14} - 1^7 = 0

Common Mistakes

Avoid these frequent errors
  • Dividing both sides by the variable term
    Don't divide both sides by x7 x^7 to get x71=0 x^7 - 1 = 0 = you lose the solution x = 0! Division by a variable eliminates solutions where that variable equals zero. Always factor out common terms instead of dividing by them.

Practice Quiz

Test your knowledge with interactive questions

Solve the following equation:


\( 2x^2-8=x^2+4 \)

FAQ

Everything you need to know about this question

Why do I get two solutions instead of one?

+

When you factor and get x7(x71)=0 x^7(x^7-1) = 0 , you have a product equal to zero. This means either factor can be zero, giving you two separate equations to solve: x7=0 x^7 = 0 and x71=0 x^7 - 1 = 0 .

How do I know what power to factor out?

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Always factor out the lowest power that appears in the equation. Here, both x14 x^{14} and x7 x^7 contain x7 x^7 , so that's your common factor!

What does it mean to take the 7th root?

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Taking the 7th root 7 \sqrt[7]{} is the opposite operation of raising to the 7th power. Since x7=0 x^7 = 0 , we get x=07=0 x = \sqrt[7]{0} = 0 . Similarly, x7=1 x^7 = 1 gives us x=17=1 x = \sqrt[7]{1} = 1 .

Why isn't x = -1 a solution?

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Let's check: (1)14(1)7=1(1)=1+1=20 (-1)^{14} - (-1)^7 = 1 - (-1) = 1 + 1 = 2 \neq 0 . Even though (1)7=1 (-1)^7 = -1 , when we substitute back into the original equation, we don't get zero.

Can I solve this without factoring?

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You could try other methods, but factoring is the most efficient approach here. It immediately shows you the structure of the equation and reveals both solutions clearly.

How do I check my work?

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Substitute each solution back into the original equation x14x7=0 x^{14} - x^7 = 0 . For x = 0: 01407=00=0 0^{14} - 0^7 = 0 - 0 = 0 ✓ . For x = 1: 11417=11=0 1^{14} - 1^7 = 1 - 1 = 0 ✓

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