Solve (-x)² - 25: Working with Squared Negative Variables

Quadratic Equations with Perfect Square Patterns

(−x)2−(+25)= (-x)^2-(+25)=

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1

Understand the problem

(−x)2−(+25)= (-x)^2-(+25)=

2

Step-by-step solution

To solve this problem, we'll proceed as follows:

  • Step 1: Recognize that (−x)2=x2(-x)^2 = x^2.
  • Step 2: Establish the equation by substituting: x2−25=0x^2 - 25 = 0.
  • Step 3: Recognize this as a difference of squares: (x−5)(x+5)=0(x - 5)(x + 5) = 0.
  • Step 4: Solve for xx from the factors: x−5=0x - 5 = 0 and x+5=0x + 5 = 0.
  • Step 5: Find solutions: x=5x = 5 and x=−5x = -5.

Therefore, the solution to the equation is x=±5x = \pm 5.

The correct choice among the options provided is x=±5x = \pm 5.

3

Final Answer

x=±5 x=±5

Key Points to Remember

Essential concepts to master this topic
  • Rule: (−x)2=x2(-x)^2 = x^2 because negative times negative equals positive
  • Technique: Factor difference of squares: x2−25=(x−5)(x+5)=0x^2 - 25 = (x-5)(x+5) = 0
  • Check: Substitute both solutions: (−5)2−25=0(-5)^2 - 25 = 0 and (5)2−25=0(5)^2 - 25 = 0 ✓

Common Mistakes

Avoid these frequent errors
  • Thinking (-x)² equals -x²
    Don't confuse (−x)2(-x)^2 with −x2-x^2 = wrong sign! The parentheses make all the difference: (−x)2=(−1⋅x)2=(−1)2⋅x2=x2(-x)^2 = (-1 \cdot x)^2 = (-1)^2 \cdot x^2 = x^2. Always remember that squaring a negative gives positive.

Practice Quiz

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Solve:

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

FAQ

Everything you need to know about this question

Why does (-x)² equal x² instead of -x²?

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The parentheses make all the difference! (−x)2(-x)^2 means you're squaring the entire negative value, and negative times negative equals positive. So (−x)2=x2(-x)^2 = x^2.

How do I know this is a difference of squares?

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Look for the pattern a2−b2a^2 - b^2! Here we have x2−25=x2−52x^2 - 25 = x^2 - 5^2, which factors as (x−5)(x+5)(x-5)(x+5). Both terms are perfect squares separated by subtraction.

Why are there two solutions instead of one?

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Because we're solving a quadratic equation! When we factor (x−5)(x+5)=0(x-5)(x+5) = 0, either factor can equal zero. This gives us x=5x = 5 or x=−5x = -5.

What if I forgot the difference of squares formula?

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You can still solve x2=25x^2 = 25 by taking the square root of both sides. Just remember: x2=∣x∣\sqrt{x^2} = |x|, so you get x=±5x = ±5.

How do I check my answer?

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Substitute both solutions back into the original equation. For x=5x = 5: (−5)2−25=25−25=0(-5)^2 - 25 = 25 - 25 = 0 ✓. For x=−5x = -5: (−(−5))2−25=52−25=0(-(−5))^2 - 25 = 5^2 - 25 = 0 ✓.

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