Find the Missing Term in (a+?)(a+3) = a²+3a+2ab+6b

Polynomial Expansion with Missing Factors

Complete the missing element

(a+?)(a+3)=a2+3a+2ab+6b (a+?)(a+3)=a^2+3a+2ab+6b

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Complete the missing number
00:04 Let's substitute X as the unknown
00:09 Let's properly open parentheses, multiply each factor by each factor
00:29 Let's calculate the products
00:46 Let's compare the corresponding expressions
00:54 Let's reduce what we can
01:00 This is the value of X, now let's check if it fits
01:05 Let's compare the corresponding expressions, substitute the X value we found
01:13 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

Complete the missing element

(a+?)(a+3)=a2+3a+2ab+6b (a+?)(a+3)=a^2+3a+2ab+6b

2

Step-by-step solution

To solve this problem, we'll approach it by expanding and comparing terms:

  • Step 1: Apply the distributive property (FOIL method) to expand (a+?)(a+3)(a+?)(a+3).
  • Step 2: Compare each term in the expansion with the corresponding term in a2+3a+2ab+6ba^2 + 3a + 2ab + 6b.
  • Step 3: Identify and solve for the missing element.

Let's execute these steps:

Step 1: Consider the expression (a+b)(a+3)(a+ b)(a+3).

Using distributive property, it expands to:
(a+b)×(a+3)=a×a+a×3+b×a+b×3 (a + b) \times (a + 3) = a \times a + a \times 3 + b \times a + b \times 3 .

This gives us:
=a2+3a+ab+3b = a^2 + 3a + ab + 3b .

Step 2: Now, compare this expansion to the given expression a2+3a+2ab+6ba^2 + 3a + 2ab + 6b.

Step 3: From the comparison, we have:
- a2a^2 terms match.
- 3a3a terms match.
- For the abab term, abab should match 2ab2ab, implying b=2bb = 2b. Therefore, the missing term must contribute an additional bb, making it b+ab=2abb + ab = 2ab. Thus, b=2b = 2.
- For the constant term, 3b=6b3b = 6b, leading to the same conclusion.

Therefore, the solution to the problem is 2b 2b .

3

Final Answer

2b 2b

Key Points to Remember

Essential concepts to master this topic
  • FOIL Method: Expand (a+?)(a+3) using First, Outer, Inner, Last
  • Term Comparison: Match coefficients: ab term needs 2ab, so ? = 2b
  • Verification: Check (a+2b)(a+3) = a²+3a+2ab+6b matches given expression ✓

Common Mistakes

Avoid these frequent errors
  • Assuming the missing term is just b
    Don't just guess b because it appears in the result = wrong expansion! This gives ab + 3b instead of 2ab + 6b. Always expand completely and compare each coefficient systematically.

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 can't the missing term just be b?

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If the missing term were just b, then (a+b)(a+3)=a2+3a+ab+3b (a+b)(a+3) = a^2 + 3a + ab + 3b . But we need 2ab and 6b, so the missing term must be 2b!

How do I know which terms to compare?

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After expanding, match terms with the same variables and powers. Compare a² with a², a terms with a terms, and constant terms with constant terms.

What if I get confused with the FOIL method?

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Remember: First × First, Outer × Outer, Inner × Inner, Last × Last. For (a+2b)(a+3) (a+2b)(a+3) : a×a, a×3, 2b×a, 2b×3.

Can I work backwards from the given expression?

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Yes! Look at the coefficients: if you have 2ab, the missing term contributes a factor of 2 to the b. If you have 6b, that's 3 × 2b.

How do I check if 2b is definitely correct?

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Substitute and expand: (a+2b)(a+3)=a2+3a+2ab+6b (a+2b)(a+3) = a^2 + 3a + 2ab + 6b . This exactly matches the given expression, so 2b is correct!

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