Multiply Binomials: Solve (x-9)(x+√9) Step by Step

FOIL Method with Square Roots

Solve the following problem:

(x9)(x+9)= (x-9)(x+\sqrt{9})=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 Let's calculate the root
00:07 Open parentheses properly, multiply each factor by each factor
00:25 Calculate the products
00:35 Collect terms
00:42 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:

(x9)(x+9)= (x-9)(x+\sqrt{9})=

2

Step-by-step solution

In order to solve this problem, we'll follow these steps:

  • Step 1: Simplify the expression inside the binomials

  • Step 2: Apply the FOIL method to expand the product of binomials

  • Step 3: Combine like terms to find the final expression

Let's proceed to work through each step:

Step 1: Simplify the expression inside the binomials

The original expression is (x9)(x+9)(x-9)(x+\sqrt{9}). First, we simplify 9\sqrt{9}, which equals 33. Thus, the expression becomes (x9)(x+3)(x-9)(x+3).

Step 2: Apply the FOIL method to expand the product

Using the FOIL method, which stands for First, Outside, Inside, and Last, we expand as follows:

  • First: Multiply the first terms: xx=x2x \cdot x = x^2

  • Outside: Multiply the outside terms: x3=3xx \cdot 3 = 3x

  • Inside: Multiply the inside terms: 9x=9x-9 \cdot x = -9x

  • Last: Multiply the last terms: 93=27-9 \cdot 3 = -27

Step 3: Combine like terms

Now, combine the results: x2+3x9x27x^2 + 3x - 9x - 27.

Combine the like terms 3x3x and 9x-9x, resulting in 6x-6x.

The final expanded form of the expression is x26x27x^2 - 6x - 27.

Comparing our result with the given choices, the correct choice is:

x26x27 x^2-6x-27

Therefore, the solution to the problem is x26x27 x^2 - 6x - 27 .

3

Final Answer

x26x27 x^2-6x-27

Key Points to Remember

Essential concepts to master this topic
  • Simplification: Always simplify radicals first: √9 = 3
  • FOIL Method: First + Outside + Inside + Last = x² + 3x - 9x - 27
  • Check: Combine like terms: 3x - 9x = -6x gives x² - 6x - 27 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to simplify square roots before multiplying
    Don't multiply (x-9)(x+√9) directly without simplifying √9 = 3 first = wrong expansion! This leads to confusion and calculation errors. Always simplify radicals at the start to get (x-9)(x+3).

Practice Quiz

Test your knowledge with interactive questions

\( (3+20)\times(12+4)= \)

FAQ

Everything you need to know about this question

Why do I need to simplify √9 first?

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Simplifying 9=3 \sqrt{9} = 3 makes the multiplication much easier! Working with (x-9)(x+3) is simpler than trying to multiply with the radical form.

What does FOIL actually stand for?

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First, Outside, Inside, Last. It's a systematic way to multiply two binomials: multiply each term in the first binomial by each term in the second binomial.

How do I combine 3x and -9x correctly?

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Think of it as addition: 3x + (-9x) = 3x - 9x = -6x. The positive 3x minus the larger 9x gives you -6x.

Can I use a different method instead of FOIL?

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Yes! You can use the distributive property twice: x(x+3) - 9(x+3). This gives the same result but some students find FOIL easier to remember.

What if I got x² + 6x - 27 instead?

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You likely made a sign error when combining like terms. Remember: 3x9x=6x 3x - 9x = -6x , not +6x. Always be careful with positive and negative signs!

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