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Use Green's theorem to evaluate the line integral along the given positively oriented curve.

int_(C)7y^(3)dx-7x^(3)dy,quad C" is the circle "x^(2)+y^(2)=4

Use Green's theorem to evaluate the line integral along the given positively oriented curve.\newlineC7y3dx7x3dy,C is the circle x2+y2=4 \int_{C} 7 y^{3} d x-7 x^{3} d y, \quad C \text { is the circle } x^{2}+y^{2}=4

Full solution

Q. Use Green's theorem to evaluate the line integral along the given positively oriented curve.\newlineC7y3dx7x3dy,C is the circle x2+y2=4 \int_{C} 7 y^{3} d x-7 x^{3} d y, \quad C \text { is the circle } x^{2}+y^{2}=4
  1. Rephrase the problem: Step 11: Rephrase the problem.\newlinequestion_prompt: Use Green's theorem to evaluate the line integral along the given positively oriented curve for the function 7y3dx7x3dy7y^3 \, dx - 7x^3 \, dy, where CC is the circle x2+y2=4x^2 + y^2 = 4.
  2. Apply Green's theorem: Step 22: Apply Green's theorem.\newlineGreen's theorem relates a line integral around a simple, closed, positively oriented curve CC to a double integral over the plane region DD bounded by CC. Green's theorem states:\newlineCPdx+Qdy=D(QxPy)dA,\int_C P \,dx + Q \,dy = \int\int_D \left(\frac{\partial Q}{\partial x} - \frac{\partial P}{\partial y}\right) dA,\newlinewhere P=7y3P = 7y^3 and Q=7x3Q = -7x^3.
  3. Calculate partial derivatives: Step 33: Calculate partial derivatives.\newlineQx=x(7x3)=21x2\frac{\partial Q}{\partial x} = \frac{\partial}{\partial x} (-7x^3) = -21x^2,\newlinePy=y(7y3)=21y2\frac{\partial P}{\partial y} = \frac{\partial}{\partial y} (7y^3) = 21y^2.
  4. Set up the double integral: Step 44: Set up the double integral. D(21x221y2)dA\int\int_D (-21x^2 - 21y^2) \, dA.
  5. Convert to polar coordinates: Step 55: Convert to polar coordinates.\newlineSince DD is a circle of radius 22, convert the integral to polar coordinates where x=rcos(θ)x = r \cos(\theta) and y=rsin(θ)y = r \sin(\theta). Then, x2+y2=r2x^2 + y^2 = r^2 and dA=rdrdθdA = r \, dr \, d\theta.\newlineD(21r2)rdrdθ=2102π02r3drdθ\int\int_D (-21r^2) r \, dr \, d\theta = -21 \int_0^{2\pi} \int_0^2 r^3 \, dr \, d\theta.
  6. Evaluate the integral: Step 66: Evaluate the integral.\newline2102π[r4/4]02dθ=2102π(16/4)dθ=2102π4dθ=21[4θ]02π=21×8π=168π-21 \int_0^{2\pi} [r^4/4]_0^2 d\theta = -21 \int_0^{2\pi} (16/4) d\theta = -21 \int_0^{2\pi} 4 d\theta = -21 [4\theta]_0^{2\pi} = -21 \times 8\pi = -168\pi.