Chapter 7: Problem 32
The parabola \(y=x^{2}+p x+q\) intercepts the straight line \(y=2 x-3\) at a point with abscissa 1 . If the distance between the vertex of the parabola and the \(x\)-axis is least, then (a) \(p=0\) and \(q=-2\) (b) \(p=-2\) and \(q=0\) (c) least distance between the parabola and \(x\)-axis is 2 (d) least distance between the parabola and \(x\)-axis is 1
Short Answer
Step by step solution
Set up the system of equations
Substitute and solve for variables
Determine the vertex formula
Derive the vertex' height from x-axis
Find conditions for minimal vertex height
Solve for p
Calculate the minimal vertex height
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vertex of a Parabola
In the given exercise, the parabola \( y = x^2 + px + q \) has its vertex x-coordinate calculated as \( x = -\frac{p}{2} \). This x-coordinate helps us find the y-coordinate of the vertex and ultimately determine the vertex's position relative to the x-axis.
Finding the vertex's position is also key to solving optimization problems as it can represent the point of least or greatest value in a graphically represented path or area.
Intersecting Lines
In this task, the parabola \( y = x^2 + px + q \) intersects the line \( y = 2x - 3 \) at \( x = 1 \). This tells us that \( x = 1 \) is a solution to both equations simultaneously. Such a point is of great interest because it allows us to further solve or simplify equations by equating them to find missing values or coefficients.
- The intersection equation derived here is \( p + q = -2 \).
- Using the known x-coordinate helps in solving for specific unknowns in equations where two or more functions meet.
Optimization Problem
Given the parabola \( y = x^2 + px + q \), our goal was to find p and q such that the vertex height \( y = -\frac{p^2}{4} + q \) is minimized.
To solve this, it's necessary to:
- Derive a formula for the vertex's height as a function of p and q using the vertex's x-coordinate.
- Substitute relevant values to form a new equation that helps in finding optimal p and q values.
Derivative
In this scenario, we calculated the derivative of the expression \(-\frac{p^2}{4} - p - 2\) to find the value of p that minimizes the vertex's y-coordinate. The derivative, \( \frac{d}{dp} \left(-\frac{p^2}{4} - 2 - p \right) = -\frac{p}{2} - 1 \), was set to zero.
Solving \(-\frac{p}{2} - 1 = 0 \) gives us \( p = -2 \). This derivative setup helps in identifying critical points that provide local minimum or maximum values.
- The derivative is crucial for determining optimal conditions in many mathematical and practical contexts.
- The result helps confirm the set conditions where the parabola vertex's height from the x-axis is minimized.