Chapter 14: Problem 6
In Exercises \(5-10\), a planar curve \(C\) is given along with a surface \(f\) that is defined over \(C\). Evaluate the line integral \(\int_{C} f(s) d s\) $$ \begin{aligned} &C \text { is the segment of } y=3 x+2 \text { on }[1,2] ; \text { the surface is }\\\ &f(x, y)=5 x+2 y \end{aligned} $$
Short Answer
Step by step solution
Parameterize the Curve
Substitute the Parameterization into the Function
Compute ds in terms of dt
Set Up the Line Integral
Integrate
Evaluate the Definite Integral
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Parameterization
For the given line \( y = 3x + 2 \) over the interval \([1, 2]\), the parameterization involves setting \( x = t \), with \( t \) ranging from 1 to 2. Consequently, substituting \( t \) into the line equation gives \( y = 3t + 2 \).
This allows us to express the curve as a vector function \( r(t) = (t, 3t + 2) \), encapsulating both \( x \) and \( y \) coordinates in terms of the parameter \( t \). This parameterization simplifies the process of computing the line integral, by expressing both the curve and the function \( f \) in a unified format.
Vector Calculus
In this scenario, the problem involves calculating a line integral, which is a type of integral that finds the sum of function values along a curve. The expression \( \int_{C} f(s) \ ds \) indicates a line integral where \( C \) is the curve and \( f(s) \) a function defined over \( C \).
Vector calculus provides the framework to transition from integrating over simple intervals to integrating over paths determined by vector-valued functions. This becomes evident in the calculation of \( ds \), which involves the derivative of the parameterized function \( r(t) \), helping us compute the integral effectively.
Surface Integral
Surface integrals are especially useful when evaluating fields over surfaces, such as flux calculations. In the context of this exercise, the function \( f(x, y) = 5x + 2y \) is evaluated over the line, but analogously, it could be extended to surfaces where surface integrals would be applied.
By learning about surface integrals, students can generalize integration techniques from one-dimensional paths to two-dimensional surfaces, preparing them for more advanced applications in physics and engineering.
Integration Techniques
The process involves substituting parameterized expressions into the integral. For instance, substituting \( f(t) = 11t + 4 \) and finding \( ds = \sqrt{10} \, dt \), the integral converts to \( \int_{1}^{2} (11t + 4) \sqrt{10} \, dt \).
The next step involves using techniques such as the power rule and the properties of definite integrals to solve. By integrating term by term, the integral becomes understandable and easier to evaluate. Splitting the integral into smaller parts forms a cumulative result, demonstrating how these techniques apply in practice to resolve problems within vector calculus.