Find the Missing Term in (x+?)(x-8) = x²-5x-24: Binomial Expansion

Binomial Expansion with Missing Coefficients

Complete the missing element

(x+?)(x8)=x25x24 (x+?)(x-8)=x^2-5x-24

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:09 First, let's fill in the missing part of the equation.
00:14 We'll use Y to represent the unknown value.
00:21 Next, open the parentheses. And multiply each term with every other term.
00:36 Now, simplify where you can. And gather similar terms together.
00:52 Then, factor out any common terms.
01:01 Finally, let's isolate Y to find its value.
01:05 And there you have it, we've solved the problem!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Complete the missing element

(x+?)(x8)=x25x24 (x+?)(x-8)=x^2-5x-24

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Expand the expression (x+?)(x8)(x+?)(x-8).
  • Step 2: Compare the expanded expression to the given quadratic expression.
  • Step 3: Determine the missing term by matching coefficients.

Now, let's work through each step:

Step 1: Write the left expression as (x+b)(x8)=x28x+bx8b(x+b)(x-8) = x^2 - 8x + bx - 8b.

Step 2: Compare the expanded form, x2+(b8)x8bx^2 + (b-8)x - 8b, to the given x25x24x^2 - 5x - 24.

Step 3: We see that the coefficients for xx should match, so we have b8=5b-8 = -5. Solving for bb, we get:

  • b8=5b=5+8b=3b - 8 = -5 \rightarrow b = -5 + 8 \rightarrow b = 3.

Optionally, verify by comparing the constant terms: 8b=24b=3-8b = -24 \rightarrow b = 3.

Therefore, the missing element in the binomial is 3 \boxed{3} .

3

Final Answer

3 3

Key Points to Remember

Essential concepts to master this topic
  • Expansion Rule: Use FOIL to expand (x+a)(x+b) = x²+(a+b)x+ab
  • Coefficient Match: Compare x-term: b-8 = -5, so b = 3
  • Verification: Check constant term: -8(3) = -24 matches given equation ✓

Common Mistakes

Avoid these frequent errors
  • Trying to factor the right side first
    Don't start by factoring x²-5x-24 = wrong approach! This makes the problem harder and can lead to calculation errors. Always expand the left side using FOIL and match coefficients directly.

Practice Quiz

Test your knowledge with interactive questions

It is possible to use the distributive property to simplify the expression below?

What is its simplified form?

\( (ab)(c d) \)

\( \)

FAQ

Everything you need to know about this question

Why do I need to use FOIL here?

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FOIL helps you systematically expand (x+?)(x8)(x+?)(x-8) to get all terms. Without it, you might miss terms or make sign errors when multiplying.

How do I know which coefficients to compare?

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Match terms with the same degree! Compare the x2x^2 terms, then the xx terms, then the constant terms. Each pair must be equal.

What if I get a different answer when checking the constant term?

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If your answers don't match, double-check your algebra! The missing value should satisfy both the x-coefficient and constant term conditions.

Can I solve this by guessing and checking?

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While guessing might work, algebraic methods are faster and more reliable. Plus, they help you understand the underlying mathematics better!

What does the question mark represent exactly?

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The ? represents the missing coefficient in the first binomial. It's the number that, when combined with x, gives us the correct expanded form.

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