Verify the Equation: (x+5)(x+3) = x²-3²

Polynomial Expansion with Equation Verification

(x+5)(x+3)=x232 (x+5)(x+3)=x^2-3^2

Is the equation a true or false statement?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Is the equation correct?
00:21 Let's use the shortened multiplication formulas
00:35 Let's divide by the common factor
00:51 Let's reduce what we can
00:59 We can see that the expressions are not equal
01:02 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

(x+5)(x+3)=x232 (x+5)(x+3)=x^2-3^2

Is the equation a true or false statement?

2

Step-by-step solution

To assess whether the equation (x+5)(x+3)=x232(x+5)(x+3) = x^2 - 3^2 is a true or false statement, we follow these steps:

  • Step 1: Expand the left side using distributive property (FOIL).
  • Step 2: Simplify the expression.
  • Step 3: Simplify the right side.
  • Step 4: Compare both sides of the equation.

Step 1: Expand (x+5)(x+3)(x+5)(x+3):
(x+5)(x+3)=x(x+3)+5(x+3)(x+5)(x+3) = x(x+3) + 5(x+3)
=x2+3x+5x+15= x^2 + 3x + 5x + 15

Step 2: Simplify this expression:
x2+3x+5x+15=x2+8x+15x^2 + 3x + 5x + 15 = x^2 + 8x + 15

Step 3: Evaluate the right side:
x232=x29x^2 - 3^2 = x^2 - 9

Step 4: Compare x2+8x+15x^2 + 8x + 15 to x29x^2 - 9:
Clearly, x2+8x+15x29x^2 + 8x + 15 \neq x^2 - 9, as the former includes the terms 8x+158x + 15, while the latter is simply reduced by 9.

Therefore, the equation (x+5)(x+3)=x232(x+5)(x+3) = x^2 - 3^2 is a Lie (false statement) because the left and right sides do not match for any value of xx.

3

Final Answer

Lie

Key Points to Remember

Essential concepts to master this topic
  • Rule: Use FOIL method to expand (a+b)(c+d) completely
  • Technique: (x+5)(x+3) = x² + 3x + 5x + 15 = x² + 8x + 15
  • Check: Compare final expanded forms: x² + 8x + 15 ≠ x² - 9 ✓

Common Mistakes

Avoid these frequent errors
  • Assuming equations are true without expanding both sides
    Don't just look at the equation and guess it's true = wrong conclusion! The forms look different but you must expand to compare properly. Always expand both sides completely and compare every term.

Practice Quiz

Test your knowledge with interactive questions

Solve:

\( (2+x)(2-x)=0 \)

FAQ

Everything you need to know about this question

Why can't I just cancel out the x² terms on both sides?

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You can only cancel terms when they appear on both sides with the same coefficient. Here, the left side has additional terms (8x + 15) that don't exist on the right side.

Could there be a special value of x that makes this equation true?

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Let's check! Set x² + 8x + 15 = x² - 9. This gives us 8x + 15 = -9, so 8x = -24, and x = -3. But even at x = -3, we get different values on each side!

How do I know when to expand vs when to factor?

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If you're asked to verify an equation, always expand to compare. If you're solving for x, you might factor. The problem type determines your approach!

What's the difference between 'true' and 'identity'?

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An equation is true for specific x-values, but an identity is true for ALL x-values. Since this equation isn't true for any x-value, it's neither!

Why does FOIL give me four terms but I only end up with three?

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Great observation! FOIL gives you four products, but some terms are like terms that combine. Here, +3x and +5x combine to make +8x.

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