/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 3 Evaluate the given integral alon... [FREE SOLUTION] | 91Ó°ÊÓ

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Evaluate the given integral along the indicated contour. \(\int_{C} z^{2} d z\), where \(C\) is \(z(t)=3 t+2 i t,-2 \leq t \leq 2\)

Short Answer

Expert verified
The integral evaluates to \(\frac{736i}{3}\).

Step by step solution

01

Express the curve parameterization

The contour \(C\) is given by the equation \(z(t) = 3t + 2it\) where \(-2 \leq t \leq 2\). We will use this parameterization to express \(z^2\) and \(dz\) in terms of \(t\).
02

Calculate \(z(t)^2\)

Calculate the square of the parameterized curve: \(z(t) = 3t + 2it\). Then, \(z(t)^2 = (3t + 2it)^2 = (3t)^2 + 2(3t)(2it) + (2it)^2 = 9t^2 + 12it^2 - 4t^2 = 5t^2 + 12it^2 = (5 + 12i)t^2\).
03

Compute \(dz\) in terms of \(dt\)

Differentiate \(z(t) = 3t + 2it\) with respect to \(t\): \( \frac{dz}{dt} = 3 + 2i\). Multiply both sides by \(dt\) to express \(dz\) as \(dz = (3 + 2i)dt\).
04

Setup the integral with limits and solve

The integral is then \(\int_{C} z^2 \, dz = \int_{-2}^{2} ((5 + 12i)t^2)(3 + 2i) \, dt\). This expands to \(\int_{-2}^{2} ((15 + 10i + 36i + 24i^2)t^2) \, dt\). Simplify \(24i^2 = -24\) yielding \((-9 + 46i)t^2\).
05

Compute the final expression

Now integrate each part separately: \(\int_{-2}^{2} (-9t^2) \, dt + \int_{-2}^{2} (46it^2) \, dt\). For \(-9t^2\), integrate to get \(-3t^3\) evaluated from -2 to 2. For \(46it^2\), integrate to get \(\frac{46i}{3}t^3\) evaluated from -2 to 2. Perform the calculations for each part.
06

Evaluate the integrals

For \(-3t^3|_{-2}^{2}\), calculate \((-3)(2)^3 - (-3)(-2)^3 = -24 + 24 = 0\). For \(\frac{46i}{3}t^3|_{-2}^{2}\), calculate \(\frac{46i}{3}(8) - \frac{46i}{3}(-8) = \frac{368i}{3} + \frac{368i}{3} = \frac{736i}{3}\).
07

Final Result

Thus, the integral \(\int_{C} z^2 \, dz = 0 + \frac{736i}{3} = \frac{736i}{3}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Contour Integration
Contour integration is a fundamental technique used in complex analysis to integrate functions over a path or contour in the complex plane. When dealing with contour integrals, our primary goal is to express the integral in terms of a parameterization of the contour. In our exercise, the contour \(C\) is parameterized by \(z(t) = 3t + 2it\), which maps points \(t\) in the interval \([-2, 2]\) onto the curve \(C\). Once the contour and the parameterization have been determined, the integral transforms from a line integral in the complex plane to a real integral of a real variable. This allows us to compute the integral using standard calculus techniques. The entire process involves substituting the parameterized expressions into the integral, as we saw in the exercise where \(z^2\) and \(dz\) were expressed in terms of \(t\). This method simplifies complicated contour integrals so they become manageable, enabling us to focus on integration techniques we're already familiar with from real calculus.
Complex Analysis
Complex analysis is a branch of mathematics that studies functions of complex variables. In this field, functions are often examined based on their behavior as polynomials of the form \( z^n \) where \( z \) is a complex number. This provides a rich framework for exploring functions’ properties, including differentiability, integrability, and continuity in the complex plane. A key advantage of complex analysis is the ability to use powerful theoretical results, such as the Cauchy Integral Theorem and Cauchy Integral Formula, which simplify the evaluation of complex integrals dramatically. These theoretical tools allow complex integrations that would be very challenging—if not impossible—in the realm of real numbers. In practice, understanding complex analysis involves more than just dealing with imaginary units \(i\). It's about visualizing functions in two dimensions, respecting the roles of both the real and imaginary parts of complex numbers, and analyzing their behavior in a holistic manner. By applying complex analysis techniques, integrals once complex or seemingly unsolvable become easier to evaluate systematically.
Parameterization of Curves
Parameterization is a method used to represent curves through equations that express the position of points on the curve as functions of one or more parameters. This approach is particularly useful in complex analysis where curves on the complex plane can be parameterized over a real interval. In the given problem, the curve \(C\) is parameterized by \(z(t) = 3t + 2it\), where \(t\) lies between \(-2\) and \(2\). This representation converts the multidimensional problem into a single-variable problem, allowing us to apply calculus techniques more easily. Parameterizing a curve involves selecting a method to trace a path across points in a specific manner, effectively encoding the curve's geometry into a simple numerical form. The benefits of parameterization are numerous, as it facilitates the rewriting of complex integrals and differential equations into forms that are easier to manage and solve. Additionally, this approach helps us visualize how the path is traversed by the parameter as its value changes, offering insights into both the geometry and the algebra of the curve.

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Most popular questions from this chapter

Use any of the results in this section to evaluate the given integral along the indicated closed contour(s). $$ \oint_{C} \operatorname{Ln}(z+10) d z ;|z|=2 $$

Suppose \(z_{0}\) is any constant complex number interior to any simple closed curve contour \(C\). Show that for a positive integer \(n\), $$ \oint_{C} \frac{d z}{\left(z-z_{0}\right)^{n}}=\left\\{\begin{array}{ll} 2 \pi i, & n=1 \\ 0, & n>1 \end{array}\right. $$

The flow described by the velocity field \(f(z)=(a+i b) / \bar{z}\) is said to have a vortex at \(z=0 .\) The geometric nature of the streamlines depends on the choice of \(a\) and \(b\). (a) Show that if \(z(t)=x(t)+i y(t)\) is the path of a particle in the flow, then $$ \begin{aligned} &\frac{d x}{d t}=\frac{a x-b y}{x^{2}+y^{2}} \\ &\frac{d y}{d t}=\frac{b x+a y}{x^{2}+y^{2}} \end{aligned} $$ (b) Rectangular and polar coordinates are related by \(r^{2}=x^{2}+y^{2}\), tan \(\theta=y / x\). Use these equations to show that $$ \frac{d r}{d t}-\frac{1}{r}\left(x \frac{d x}{d t}+y \frac{d y}{d t}\right), \frac{d \theta}{d t}-\frac{1}{r^{2}}\left(-y \frac{d x}{d t}+x \frac{d y}{d t}\right) $$ (c) Use the equations in parts (a) and (b) to establish that $$ \frac{d r}{d t}=\frac{a}{r}, \frac{d \theta}{d t}=\frac{b}{r^{2}} $$ (d) Use the equations in part (c) to conclude that the streamlines of the flow are logarithmic spirals \(r=c e^{a \theta / b}, b \neq 0 .\) Use a graphing utility to verify that a particle traverses a path in a counterclockwise direction if and only if \(a<0\), and in a clockwise direction if and only if \(b<0 .\) Which of these directions corresponds to motion spiraling into the vortex?

Evaluate \(\int_{C} y d x+x d y\) on the given curve from \((0,0)\) to \((1,1)\). \(C\) consists of the line segments from \((0,0)\) to \((0,1)\) and from \((0,1)\) to \((1,1)\).

Use any of the results in this section to evaluate the given integral along the indicated closed contour(s). \(\oint_{C} \frac{-3 z+2}{z^{2}-8 z+12} d z\) (a) \(|z-5|=2\), (b) \(|z|=9\)

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