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
00:09 Let's solve the problem together.
00:13 We'll begin by finding the root, step by step.
00:18 First, open the parentheses correctly. Multiply each factor by eac h other. Take your time with this par t.
00:34 Next, calculate all the products carefully.
00:44 Now, collect all the similar terms.
00:51 Great job! And that's how we find the solution to this 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

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 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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