Solve the Equation: 8x - x⁴ = 0 | Fourth-Degree Polynomial

Factoring Polynomials with Zero Product Property

Solve the following problem:

8xx4=0 8x-x^4=0

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:07 First, we need to find the value of X.
00:12 Let's factor the expression to find term X.
00:15 Next, we'll take out the common factor from the parentheses.
00:25 This gives us one solution that makes the equation zero.
00:30 Now, let's check which solutions make the second term zero.
00:34 We'll isolate X, and then take the cube root. Ready?
00:49 Break down the number 8, to 2 to the power of 3.
00:53 And that's how we solve this problem. Great job!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the following problem:

8xx4=0 8x-x^4=0

2

Step-by-step solution

Shown below is the given equation:

8xx4=0 8x-x^4=0

Note that on the left side we are able to factor the expression by using a common factor. The largest common factor for the numbers and variables in this case is x x due to the fact that the first power is the lowest power in the equation. Therefore it is included both in the term with the fourth power and in the term with the first power. Any power higher than this is not included in the term with the first power, which is the lowest. Hence this is the term with the highest power that can be factored out as a common factor from all terms in the expression. Continue to factor the expression:

8xx4=0x(8x3)=0 8x-x^4=0 \\ \downarrow\\ x(8-x^3)=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, given 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:

x=0 \boxed{x=0}

or:

8x3=08=x3/3x=2 8-x^3=0\\ 8=x^3\hspace{8pt}\text{/}\sqrt[3]{\hspace{6pt}}\\ \downarrow\\ \boxed{x=2} (in this case taking the odd root of the left side of the equation will yield only one possibility)

Let's summarize the solution of the equation:

8xx4=0x(8x3)=0x=08x3=0x=2x=0,2 8x-x^4=0 \\ \downarrow\\ x(8-x^3)=0 \\ \downarrow\\ \boxed{ x=0}\\ 8-x^3=0 \rightarrow \boxed{x=2}\\ \downarrow\\ \boxed{x=0,2}

Therefore the correct answer is answer A.

3

Final Answer

x=0,2 x=0,2

Key Points to Remember

Essential concepts to master this topic
  • Factoring: Extract common factor x from all terms first
  • Technique: Factor 8xx4=x(8x3) 8x-x^4=x(8-x^3) then solve each part
  • Check: Substitute x=0: 8(0)-0⁴=0 ✓ and x=2: 8(2)-2⁴=0 ✓

Common Mistakes

Avoid these frequent errors
  • Dividing both sides by x immediately
    Don't divide 8x-x⁴=0 by x to get 8-x³=0! This eliminates the solution x=0 completely. Always factor out the common factor first, then use zero product property to find ALL solutions.

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 can't I just divide both sides by x?

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Dividing by x would lose the solution x=0! When you divide by a variable, you assume it's not zero, which eliminates zero as a possible answer. Always factor first instead.

How do I know what to factor out?

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Look for the lowest power of x that appears in every term. Here, x¹ appears in both 8x and x⁴, so factor out x: x(8x3) x(8-x^3)

What is the zero product property?

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If a×b=0 a \times b = 0 , then either a=0 or b=0 (or both). So when x(8x3)=0 x(8-x^3)=0 , either x=0 or 8-x³=0.

Why does x³=8 give only x=2?

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The cube root of 8 is 2 because 2³=8. Unlike even roots, odd roots like cube roots have only one real solution for any real number.

How can I check if x=2 is really correct?

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Substitute into the original equation: 8(2)(2)4=1616=0 8(2)-(2)^4 = 16-16 = 0 ✓ . Both sides equal zero, so x=2 is correct!

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