Verify the Rational Expression: Is (-x+7)/(x-7) = 1 Correct?

Rational Expression Simplification with Domain Restrictions

Determine if the simplification below is correct:

x+7x7=1 \frac{-x+7}{x-7}=1

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Determine if the reduction is correct
00:03 Take out the minus from the parentheses
00:14 Reduce what we can, when reducing the entire fraction there's always 1 remaining
00:19 In this case (-1) will remain due to the minus we took out from the parentheses
00:23 Compare between the expressions
00:31 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

Determine if the simplification below is correct:

x+7x7=1 \frac{-x+7}{x-7}=1

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Simplify the equation x+7=x7-x + 7 = x - 7.
  • Step 2: Solve for xx to verify if the equation holds true.

Now, let's work through each step:
Step 1: Starting with the equation x+7=x7-x + 7 = x - 7, we'll simplify by adding xx to both sides:
x+7+x=x7+x-x + 7 + x = x - 7 + x
This simplifies to 7=2x77 = 2x - 7.
Next, add 7 to both sides to further simplify:
7+7=2x7+77 + 7 = 2x - 7 + 7
This gives 14=2x14 = 2x.
Step 2: Divide both sides by 2 to solve for xx:
x=142x = \frac{14}{2}
Thus, x=7x = 7.

However, substituting x=7x = 7 into the original expression x+7x7\frac{-x + 7}{x - 7} results in division by zero, which is undefined. Therefore, x+7-x + 7 cannot be equal to x7x - 7 for all values of xx, and the simplification of the expression to 1 is incorrect under normal mathematical rules.

The simplification provided in the problem is incorrect.

3

Final Answer

Incorrect

Key Points to Remember

Essential concepts to master this topic
  • Domain Check: Expression undefined when denominator equals zero
  • Technique: Factor numerator -x+7 = -(x-7) for comparison
  • Verification: Test if (x7)x7=1 \frac{-(x-7)}{x-7} = -1 for all valid x ✓

Common Mistakes

Avoid these frequent errors
  • Ignoring domain restrictions when simplifying
    Don't assume x+7x7=1 \frac{-x+7}{x-7} = 1 without checking domain restrictions! When x = 7, the denominator becomes zero making the expression undefined. Always identify values that make denominators zero before simplifying rational expressions.

Practice Quiz

Test your knowledge with interactive questions

Determine if the simplification shown below is correct:

\( \frac{7}{7\cdot8}=8 \)

FAQ

Everything you need to know about this question

Why can't I just cancel out terms to get 1?

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You can't cancel terms that aren't common factors! The numerator -x+7 and denominator x-7 are not identical. Factor the numerator first: -x+7 = -(x-7), giving you (x7)x7=1 \frac{-(x-7)}{x-7} = -1 (not +1).

What happens when x = 7 in this expression?

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When x = 7, the denominator becomes 7-7 = 0, making the expression undefined. Division by zero is never allowed in mathematics, so x = 7 is not in the domain of this function.

How do I know if a rational expression equals a constant?

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First check the domain restrictions, then simplify by factoring. If the simplified form has no variables left (like getting -1), then it equals that constant for all valid x values.

Is -x+7 the same as -(x-7)?

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Yes! You can factor out the negative: -x+7 = -x+7 = -(x-7). This factoring helps you see the relationship between numerator and denominator clearly.

Can this expression ever equal 1?

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No! After proper simplification, x+7x7=1 \frac{-x+7}{x-7} = -1 for all values where x ≠ 7. The expression is always -1, never +1.

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