Chapter 2: Problem 49
Use a graphing utility to make rough estimates of the locations of all horizontal tangent lines, and then find their exact locations by differentiating. \(y=\frac{1}{3} x^{3}-\frac{3}{2} x^{2}+2 x\)
Short Answer
Expert verified
Horizontal tangent lines are at points (1, 5/6) and (2, 2/3).
Step by step solution
01
Graph the Function
First, plot the function \(y=\frac{1}{3}x^3-\frac{3}{2}x^2+2x\) using a graphing utility. Look for points where the slope of the tangent line appears to be zero; these will be your rough estimates for horizontal tangents.
02
Set the Derivative to Zero
To find the exact locations of the horizontal tangent lines, differentiate the function: \(y' = x^2 - 3x + 2\). Set this derivative equal to zero to solve for \(x\): \[x^2 - 3x + 2 = 0\]
03
Solve the Quadratic Equation
Solve the quadratic equation \(x^2 - 3x + 2 = 0\) using the quadratic formula: \[x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}\] Here, \(a = 1\), \(b = -3\), and \(c = 2\). Calculate the discriminant and find the roots: \[x = \frac{3 \pm \sqrt{9-8}}{2}\] \[x = \frac{3 \pm 1}{2}\]
04
Find the Exact X-Values
From the last step, solve the two parts of the equation to get the roots: 1. \(x = \frac{3+1}{2} = 2\) 2. \(x = \frac{3-1}{2} = 1\) Thus, the exact \(x\)-values where horizontal tangents occur are \(x = 1\) and \(x = 2\).
05
Find the Corresponding Y-Values
Substitute \(x = 1\) and \(x = 2\) back into the original function to find the corresponding \(y\)-values. For \(x = 1\): \[y = \frac{1}{3}(1)^3 - \frac{3}{2}(1)^2 + 2(1) = \frac{1}{3} - \frac{3}{2} + 2 = \frac{5}{6}\] For \(x = 2\): \[y = \frac{1}{3}(2)^3 - \frac{3}{2}(2)^2 + 2(2) = \frac{8}{3} - 6 + 4 = \frac{2}{3}\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Graphing Functions
Graphing functions involves plotting points on a coordinate plane to visually represent a mathematical equation. This visualization helps in understanding the behavior of the function. For the given function \(y=\frac{1}{3} x^{3}-\frac{3}{2} x^{2}+2 x\), using a graphing utility is a great way to identify where horizontal tangent lines might occur.When graphing, pay attention to:
- The shape of the graph: This function, being a cubic polynomial, will likely have two turning points.
- Where the curve appears to flatten out, or plateau—these areas are candidates for horizontal tangents.
Differentiation
Differentiation is a core concept in calculus used to find the rate at which one quantity changes with respect to another. It is the process of finding the derivative of a function. The derivative represents the slope of the tangent line to the curve at any given point.In the context of our function:- The original equation is \(y=\frac{1}{3} x^{3}-\frac{3}{2} x^{2}+2 x\).- Its derivative, \(y' = x^2 - 3x + 2\), gives us another equation representing the slope of the curve at any point.- For horizontal tangent lines, which have a slope of zero, the derivative \(y'\) is set to zero, resulting in the equation \(x^2 - 3x + 2 = 0\). Solving this derivative equation reveals where the function has horizontal tangents, a legendary calculus problem helping students join the dots between graphs and derivatives.
Quadratic Equations
Quadratic equations are polynomial equations of the form \(ax^2 + bx + c = 0\). Solving them is fundamental to understanding various algebraic problems.For our differentiated equation \(x^2 - 3x + 2 = 0\):
- Recognize \(a = 1\), \(b = -3\), \(c = 2\).
- Use the quadratic formula \(x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}\) to find the roots of the equation.