Question 19 of 480
If (a2b−3c)3/4a−1b4c5 = apbqcr; what is the value of p+2q?
- A. (5/2)
- B. -(5/4)
- C. -(25/4)
- D. -10
Correct Answer:
D
Explanation
To solve the problem, we need to simplify the expression given and find the values of \( p \), \( q \), and \( r \) in the expression \( a^p b^q c^r \). Then, we will calculate \( p + 2q \).
### Step 1: Simplifying the Expression
The expression we need to simplify is:
\[
\frac{(a^2 b^{-3} c)^{3/4}}{a^{-1} b^4 c^5}
\]
#### Step 1.1: Simplifying the Numerator
First, let's simplify the numerator \( (a^2 b^{-3} c)^{3/4} \):
1. **Apply the exponent**: When raising a product to a power, we distribute the exponent to each factor:
\[
(a^2)^{3/4} (b^{-3})^{3/4} (c)^{3/4} = a^{2 \cdot \frac{3}{4}} b^{-3 \cdot \frac{3}{4}} c^{1 \cdot \frac{3}{4}}
\]
This simplifies to:
\[
a^{\frac{3}{2}} b^{-\frac{9}{4}} c^{\frac{3}{4}}
\]
#### Step 1.2: Simplifying the Denominator
Now, let's simplify the denominator \( a^{-1} b^4 c^5 \):
- This is already in its simplest form:
\[
a^{-1} b^4 c^5
\]
### Step 2: Combining the Numerator and Denominator
Now we can combine the simplified numerator and denominator:
\[
\frac{a^{\frac{3}{2}} b^{-\frac{9}{4}} c^{\frac{3}{4}}}{a^{-1} b^4 c^5}
\]
#### Step 2.1: Applying the Quotient Rule
Using the quotient rule \( \frac{x^m}{x^n} = x^{m-n} \), we simplify each base:
1. For \( a \):
\[
a^{\frac{3}{2} - (-1)} = a^{\frac{3}{2} + 1} = a^{\frac{3}{2} + \frac{2}{2}} = a^{\frac{5}{2}}
\]
2. For \( b \):
\[
b^{-\frac{9}{4} - 4} = b^{-\frac{9}{4} - \frac{16}{4}} = b^{-\frac{25}{4}}
\]
3. For \( c \):
\[
c^{\frac{3}{4} - 5} = c^{\frac{3}{4} - \frac{20}{4}} = c^{-\frac{17}{4}}
\]
### Step 3: Final Expression
Combining these results, we have:
\[
\frac{(a^2 b^{-3} c)^{3/4}}{a^{-1} b^4 c^5} = a^{\frac{5}{2}} b^{-\frac{25}{4}} c^{-\frac{17}{4}}
\]
This can be expressed as:
\[
a^{\frac{5}{2}} b^{-\frac{25}{4}} c^{-\frac{17}{4}} = a^p b^q c^r
\]
Where:
- \( p = \frac{5}{2} \)
- \( q = -\frac{25}{4} \)
- \( r = -\frac{17}{4} \)
### Step 4: Calculating \( p + 2q \)
Now we need to calculate \( p + 2q \):
\[
p + 2q = \frac{5}{2} + 2 \left(-\frac{25}{4}\right)
\]
Calculating \( 2q \):
\[
2q = 2 \cdot -\frac{25}{4} = -\frac{50}{4} = -\frac{25}{2}
\]
Now, substituting back into the equation:
\[
p + 2q = \frac{5}{2} - \frac{25}{2} = \frac{5 - 25}{2} = \frac{-20}{2} = -10
\]
### Conclusion
Thus, the final answer is:
\[
\boxed{-10}
\]
### Explanation of Other Options
- **Option A: \( \frac{5}{2} \)**: This is incorrect because it does not account for the negative contributions from \( q \) and \( r \).
- **Option B: \( -\frac{5}{4} \)**: This is also incorrect as it underestimates the negative impact of \( q \).
- **Option C: \( -\frac{25}{4} \)**: This is incorrect because it does not correctly combine \( p \) and \( 2q \).
### Revision Summary
- Simplify expressions using exponent rules and the quotient rule.
- Combine like bases by subtracting exponents.
- Carefully calculate \( p + 2q \) using the values derived from the simplified expression.
- Always check each step to avoid common pitfalls in exponent manipulation.