Convert (x+1)(x-1) to Its Standard Quadratic Form

Polynomial Expansion with Special Products

Find the standard representation of the following function

f(x)=(x+1)(x1) f(x)=(x+1)(x-1)

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Simplified to the standard representation of the function
00:04 Let's expand the brackets according to the shortened multiplication formulas
00:14 We will use this formula in our exercise
00:26 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

Find the standard representation of the following function

f(x)=(x+1)(x1) f(x)=(x+1)(x-1)

2

Step-by-step solution

To solve this problem and find the standard representation of the function f(x)=(x+1)(x1) f(x) = (x+1)(x-1) , we will expand the product using the distributive property, often recalled as FOIL (First, Outer, Inner, Last) for the product of two binomials.

Let's proceed step-by-step:

  • Step 1: Apply the distributive property:
    f(x)=(x+1)(x1) f(x) = (x+1)(x-1) would become:
  • First terms: xx=x2 x \cdot x = x^2
  • Outer terms: x(1)=x x \cdot (-1) = -x
  • Inner terms: 1x=x 1 \cdot x = x
  • Last terms: 1(1)=1 1 \cdot (-1) = -1

Step 2: Combine all the terms obtained from the FOIL method:
x2x+x1 x^2 - x + x - 1

Step 3: Simplify the expression by combining like terms:
The terms x-x and xx cancel each other out, simplifying to:
f(x)=x21 f(x) = x^2 - 1

Thus, the standard representation of the function is f(x)=x21 f(x) = x^2 - 1 .

3

Final Answer

f(x)=x21 f(x)=x^2-1

Key Points to Remember

Essential concepts to master this topic
  • Rule: Use FOIL method to multiply two binomial factors
  • Technique: Recognize difference of squares: (x+1)(x1)=x212 (x+1)(x-1) = x^2 - 1^2
  • Check: Expand step-by-step and combine like terms: -x + x = 0 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to combine like terms after FOIL
    Don't stop at x2x+x1 x^2 - x + x - 1 = wrong final answer! The middle terms -x and +x must be combined. Always simplify completely by combining like terms to get x21 x^2 - 1 .

Practice Quiz

Test your knowledge with interactive questions

Create an algebraic expression based on the following parameters:

\( a=2,b=2,c=2 \)

FAQ

Everything you need to know about this question

Why do the middle terms cancel out?

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When you multiply (x+1)(x1) (x+1)(x-1) , you get -x from the outer terms and +x from the inner terms. Since they're opposites, they add to zero: -x + x = 0!

Is there a shortcut for this type of problem?

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Yes! This is a difference of squares pattern: (a+b)(ab)=a2b2 (a+b)(a-b) = a^2 - b^2 . So (x+1)(x1)=x212=x21 (x+1)(x-1) = x^2 - 1^2 = x^2 - 1 directly!

What if I get a different answer using FOIL?

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Double-check your work! Make sure you correctly multiply each pair: First (x·x), Outer (x·(-1)), Inner (1·x), and Last (1·(-1)). Then combine like terms carefully.

How do I know when I have the standard form?

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Standard form means the polynomial is written as ax2+bx+c ax^2 + bx + c with terms in descending order of powers. Your final answer x21 x^2 - 1 is already in standard form!

Why is this called a quadratic function?

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It's quadratic because the highest power of x is 2 (from the x2 x^2 term). Even though there's no x term in the final answer, it's still a quadratic function.

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