Question 18 of 480
If (a2b−3c)34a−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 equation
\[
\frac{(a^2 b^{-3}c)^{\frac{3}{4}}}{a^{-1}b^{4}c^{5}}=a^{p} b^{q} c^{r}
\]
and find the value of \( p + 2q \), we will break down the problem step-by-step.
### Step 1: Simplify the Left Side
First, we need to simplify the left side of the equation. We start with the numerator:
\[
(a^2 b^{-3}c)^{\frac{3}{4}}
\]
Using the power of a product rule \((xy)^n = x^n y^n\), we can distribute the exponent \(\frac{3}{4}\):
\[
= a^{2 \cdot \frac{3}{4}} b^{-3 \cdot \frac{3}{4}} c^{1 \cdot \frac{3}{4}} = a^{\frac{3}{2}} b^{-\frac{9}{4}} c^{\frac{3}{4}}
\]
Now, we can rewrite the entire left side:
\[
\frac{(a^2 b^{-3}c)^{\frac{3}{4}}}{a^{-1}b^{4}c^{5}} = \frac{a^{\frac{3}{2}} b^{-\frac{9}{4}} c^{\frac{3}{4}}}{a^{-1} b^{4} c^{5}}
\]
### Step 2: Simplify the Denominator
Next, we simplify the denominator:
\[
a^{-1} b^{4} c^{5}
\]
### Step 3: Combine the Fractions
Now we can combine the fractions:
\[
= a^{\frac{3}{2} - (-1)} b^{-\frac{9}{4} - 4} c^{\frac{3}{4} - 5}
\]
Calculating each exponent:
1. For \(a\):
\[
\frac{3}{2} - (-1) = \frac{3}{2} + 1 = \frac{3}{2} + \frac{2}{2} = \frac{5}{2}
\]
2. For \(b\):
\[
-\frac{9}{4} - 4 = -\frac{9}{4} - \frac{16}{4} = -\frac{25}{4}
\]
3. For \(c\):
\[
\frac{3}{4} - 5 = \frac{3}{4} - \frac{20}{4} = -\frac{17}{4}
\]
Putting it all together, we have:
\[
\frac{(a^2 b^{-3}c)^{\frac{3}{4}}}{a^{-1}b^{4}c^{5}} = a^{\frac{5}{2}} b^{-\frac{25}{4}} c^{-\frac{17}{4}}
\]
### Step 4: Identify \(p\), \(q\), and \(r\)
From the equation
\[
a^{\frac{5}{2}} b^{-\frac{25}{4}} c^{-\frac{17}{4}} = a^{p} b^{q} c^{r}
\]
we can identify:
- \(p = \frac{5}{2}\)
- \(q = -\frac{25}{4}\)
- \(r = -\frac{17}{4}\)
### Step 5: Calculate \(p + 2q\)
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 value of \(p + 2q\) 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 \(q\).
- **Option B: \(-\frac{5}{4}\)** - This is incorrect as it underestimates the negative impact of \(q\).
- **Option C: \(-\frac{25}{4}\)** - This is incorrect as it miscalculates the contributions from both \(p\) and \(q\).
### Revision Summary
- Simplify expressions using exponent rules.
- Combine fractions by subtracting exponents.
- Identify coefficients \(p\), \(q\), and \(r\) from the simplified expression.
- Carefully calculate \(p + 2q\) to avoid arithmetic errors.