Question 53 of 480
Simplify 3(2n+1)−4(2n−1)2n+1−2n
- A. 2n+1
- B. 2n-1
- C. 4
- D. 1/4
Correct Answer:
C
Explanation
To simplify the expression
\[
\frac{3(2^{n+1}) - 4(2^{n-1})}{2^{n+1} - 2^n}
\]
let's break it down step by step.
### Step 1: Simplify the Numerator
The numerator is
\[
3(2^{n+1}) - 4(2^{n-1}).
\]
We can rewrite \(2^{n+1}\) and \(2^{n-1}\) in terms of \(2^n\):
- \(2^{n+1} = 2 \cdot 2^n\)
- \(2^{n-1} = \frac{2^n}{2}\)
Substituting these into the numerator gives:
\[
3(2 \cdot 2^n) - 4\left(\frac{2^n}{2}\right) = 6 \cdot 2^n - 2 \cdot 2^n = (6 - 2) \cdot 2^n = 4 \cdot 2^n.
\]
### Step 2: Simplify the Denominator
The denominator is
\[
2^{n+1} - 2^n.
\]
Using the same substitution as before:
\[
2^{n+1} - 2^n = 2 \cdot 2^n - 2^n = (2 - 1) \cdot 2^n = 1 \cdot 2^n = 2^n.
\]
### Step 3: Combine the Simplified Parts
Now we can substitute the simplified numerator and denominator back into the fraction:
\[
\frac{4 \cdot 2^n}{2^n}.
\]
### Step 4: Cancel Common Terms
Since \(2^n\) is in both the numerator and the denominator, we can cancel it out:
\[
\frac{4 \cdot 2^n}{2^n} = 4.
\]
### Conclusion
Thus, the simplified expression is
\[
4.
\]
### Answer
The correct option is **C. 4**.
### Explanation of Other Options
- **A. 2n + 1**: This option suggests a linear expression in terms of \(n\). However, our simplification led us to a constant value of 4, not a function of \(n\).
- **B. 2n - 1**: Similar to option A, this is also a linear expression. The simplification does not yield a linear function of \(n\), so this option is incorrect.
- **D. 1/4**: This option suggests a fraction that is much smaller than our result. Since we found the simplified expression to be 4, this option is also incorrect.
### Revision Summary
- Simplify the numerator and denominator separately before combining.
- Use properties of exponents to rewrite terms for easier manipulation.
- Cancel common factors in the numerator and denominator to simplify the expression.
- The final simplified result of the given expression is **4**.