Question 92 of 480
If two graphs y = px\(^2\) + q and y = 2x\(^2\) -1 intersect at x = 2, find the value of p in terms q.
- A. \(\frac{q-8}{7}\)
- B. \(\frac{7-q}{4}\)
- C. \(\frac{8-q}{2}\)
- D. \(\frac{7+q}{8}\)
Correct Answer:
B
Explanation
To solve the problem of finding the value of \( p \) in terms of \( q \) for the graphs \( y = px^2 + q \) and \( y = 2x^2 - 1 \) that intersect at \( x = 2 \), we will follow these steps:
### Step 1: Set the equations equal to each other at the point of intersection
Since the two graphs intersect at \( x = 2 \), we can set their equations equal to each other at this point:
\[
px^2 + q = 2x^2 - 1
\]
### Step 2: Substitute \( x = 2 \) into the equations
Now, we substitute \( x = 2 \) into both equations:
1. For the first equation \( y = px^2 + q \):
\[
y = p(2^2) + q = 4p + q
\]
2. For the second equation \( y = 2x^2 - 1 \):
\[
y = 2(2^2) - 1 = 2(4) - 1 = 8 - 1 = 7
\]
### Step 3: Set the two expressions for \( y \) equal to each other
Now we have:
\[
4p + q = 7
\]
### Step 4: Solve for \( p \) in terms of \( q \)
To isolate \( p \), we can rearrange the equation:
\[
4p = 7 - q
\]
\[
p = \frac{7 - q}{4}
\]
### Conclusion: Identify the correct option
From our calculation, we find that:
\[
p = \frac{7 - q}{4}
\]
This matches option **B**.
### Step 5: Analyze the other options
Now, let's briefly analyze the other options to understand why they are incorrect:
- **Option A: \(\frac{q - 8}{7}\)**
This option suggests a different relationship between \( p \) and \( q \) that does not satisfy the equation we derived.
- **Option C: \(\frac{8 - q}{2}\)**
This option also does not align with our derived equation. If we substitute values, it does not yield the correct intersection point.
- **Option D: \(\frac{7 + q}{8}\)**
This option suggests a positive correlation between \( p \) and \( q \) that contradicts our derived relationship.
### Summary of Key Points
- We set the two equations equal at the intersection point \( x = 2 \).
- We substituted \( x = 2 \) into both equations to find their \( y \)-values.
- We derived the equation \( 4p + q = 7 \) and solved for \( p \).
- The correct answer is \( p = \frac{7 - q}{4} \), which corresponds to option **B**.
### Revision Summary
- To find intersections, set the equations equal at the given \( x \)-value.
- Substitute the \( x \)-value into both equations to find corresponding \( y \)-values.
- Rearrange the resulting equation to isolate the variable of interest.
- Always check other options to confirm the correctness of your answer.