Question

Difficulty: MediumSurds and Indices

Consider the algebraic fraction below:

5n+25n5n+15n\frac{5^{n+2} - 5^n}{5^{n+1} - 5^n}

Which of the following represents the simplified exact value of this expression?

  1. A
    4
  2. B
    5
  3. 6Answer
  4. D
    25

Answer

6
The expression can be systematically simplified by factoring out the lowest common power of the base, which is 5n5^n, from both the numerator and the denominator. The numerator becomes 5n(521)=5n(24)5^n(5^2 - 1) = 5^n(24). The denominator becomes 5n(511)=5n(4)5^n(5^1 - 1) = 5^n(4). Canceling the common factor 5n5^n from the top and bottom leaves 24/424 / 4, which equals 6.

Step-by-Step Solution

1
Identify the greatest common factor in both the numerator and the denominator.
The common factor is 5n5^n.
Factoring out the lowest power of the base simplifies algebraic expressions involving exponential terms.
2
Factor out 5n5^n from the numerator.
5n+25n=5n(521)5^{n+2} - 5^n = 5^n(5^2 - 1)
Applying the exponent rule ax+y=ax×aya^{x+y} = a^x \times a^y in reverse allows us to extract the common term.
3
Factor out 5n5^n from the denominator.
5n+15n=5n(511)5^{n+1} - 5^n = 5^n(5^1 - 1)
Applying the same extraction process to the bottom expression.
4
Substitute the factored forms back into the fraction and cancel the common 5n5^n term.
5n(251)5n(51)=244\frac{5^n(25 - 1)}{5^n(5 - 1)} = \frac{24}{4}
The 5n5^n multiplier in the numerator and denominator cancel each other out, leaving basic arithmetic values.
5
Perform the final arithmetic division.
24÷4=624 \div 4 = 6
Simplifying the remaining numerical fraction yields the final exact value.

Key Concept

Simplifying exponential expressions by factoring out common base powers.
Estimated Time:1m 15s
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