Math Problem Statement

Let a 2 R. Consider the planar curve de ned by the equation y2 = x3􀀀x+a where a is some constant parameter. Notice that for each value of a we get a di erent curve.Fix a = 2. Find out how many points on the curve have a vertical tangent line and how many points on the curve have a horizontal tangent line. Find all of their coordinates.

Solution

To analyze the curve given by the equation y2=x3x+2y^2 = x^3 - x + 2, we need to find points with vertical and horizontal tangent lines. Let’s go through the steps to determine both types of points.

Step 1: Find the Derivative

To find tangent lines, we’ll differentiate implicitly with respect to xx and solve for dydx\frac{dy}{dx} to find the slope of the tangent.

Given: y2=x3x+2y^2 = x^3 - x + 2

Differentiating both sides with respect to xx: 2ydydx=3x212y \frac{dy}{dx} = 3x^2 - 1

Solving for dydx\frac{dy}{dx}: dydx=3x212y\frac{dy}{dx} = \frac{3x^2 - 1}{2y}

Step 2: Conditions for Vertical and Horizontal Tangents

  • Horizontal Tangent: Occurs when dydx=0\frac{dy}{dx} = 0, which requires 3x21=03x^2 - 1 = 0.
  • Vertical Tangent: Occurs when the denominator 2y=02y = 0, implying y=0y = 0.

Step 3: Find Points with Horizontal Tangents

  1. Solve 3x21=03x^2 - 1 = 0: 3x2=1    x2=13    x=±133x^2 = 1 \implies x^2 = \frac{1}{3} \implies x = \pm \frac{1}{\sqrt{3}}

  2. Substitute these xx-values into the original equation to find the corresponding yy-values.

    • For x=13x = \frac{1}{\sqrt{3}}: y2=(13)313+2=13313+2=223y^2 = \left(\frac{1}{\sqrt{3}}\right)^3 - \frac{1}{\sqrt{3}} + 2 = \frac{1}{3\sqrt{3}} - \frac{1}{\sqrt{3}} + 2 = 2 - \frac{2}{\sqrt{3}}
    • Similarly, for x=13x = -\frac{1}{\sqrt{3}}.
  3. Find corresponding yy-values for both cases.

Step

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Curve Analysis
Planar Curves

Formulas

Implicit differentiation of y^2 = x^3 - x + a: 2y * (dy/dx) = 3x^2 - 1
Slope of tangent line: dy/dx = (3x^2 - 1) / (2y)
Condition for horizontal tangent: dy/dx = 0
Condition for vertical tangent: denominator of dy/dx = 0 (i.e., 2y = 0)

Theorems

Implicit Differentiation
Tangent Line Conditions (horizontal and vertical)

Suitable Grade Level

Undergraduate Calculus