Trade a line integral around a closed curve for a double integral inside it. 45 problems with worked solutions; in 45 of them every
equation is proved by a computer algebra system.
5 worked problems
Try each one before opening the solution. Every line is labeled with what checked it. How we verify
Use Green's theorem to evaluate \( \displaystyle \oint_C (x^{2} - y)\,dx + (x + y^{2})\,dy \), where C is the boundary of the rectangle \( \displaystyle [0, 3] \times [0, 1] \), counterclockwise.
Green's theorem: ∮ P dx + Q dy = ∬ (∂Q/∂x − ∂P/∂y) dA.
\[ \int\limits_{0}^{1}\int\limits_{0}^{3} 2\, dx\, dy = 6 \]
Integrate over the rectangle.✓ Proved
Answer \( 6 \)
✓ Nihil obstat Lines: 2 proved, 1 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
Use Green's theorem to evaluate \( \displaystyle \oint_C (- y^{2})\,dx + (x y)\,dy \), where C is the boundary of the rectangle \( \displaystyle [0, 1] \times [0, 3] \), counterclockwise.
Green's theorem: ∮ P dx + Q dy = ∬ (∂Q/∂x − ∂P/∂y) dA.
Reviewed
\[ - \frac{d}{d y} \left(- y^{2}\right) + \frac{\partial}{\partial x} x y = 3 y \]
∂Q/∂x − ∂P/∂y.✓ Proved
\[ \int\limits_{0}^{3}\int\limits_{0}^{1} 3 y\, dx\, dy = \frac{27}{2} \]
Integrate over the rectangle.✓ Proved
Answer \( \frac{27}{2} \)
✓ Nihil obstat Lines: 2 proved, 1 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
Use Green's theorem to evaluate \( \displaystyle \oint_C (- x y)\,dx + (x y)\,dy \), where C is the boundary of the rectangle \( \displaystyle [0, 3] \times [0, 2] \), counterclockwise.
Green's theorem: ∮ P dx + Q dy = ∬ (∂Q/∂x − ∂P/∂y) dA.
Reviewed
\[ - \frac{\partial}{\partial y} \left(- x y\right) + \frac{\partial}{\partial x} x y = x + y \]
∂Q/∂x − ∂P/∂y.✓ Proved
\[ \int\limits_{0}^{2}\int\limits_{0}^{3} \left(x + y\right)\, dx\, dy = 15 \]
Integrate over the rectangle.✓ Proved
Answer \( 15 \)
✓ Nihil obstat Lines: 2 proved, 1 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
Use Green's theorem to evaluate \( \displaystyle \oint_C (y)\,dx + (3 x)\,dy \), where C is the boundary of the rectangle \( \displaystyle [0, 1] \times [0, 2] \), counterclockwise.
Green's theorem: ∮ P dx + Q dy = ∬ (∂Q/∂x − ∂P/∂y) dA.
Reviewed
\[ \frac{d}{d x} 3 x - \frac{d}{d y} y = 2 \]
∂Q/∂x − ∂P/∂y.✓ Proved
\[ \int\limits_{0}^{2}\int\limits_{0}^{1} 2\, dx\, dy = 4 \]
Integrate over the rectangle.✓ Proved
Answer \( 4 \)
✓ Nihil obstat Lines: 2 proved, 1 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
Use Green's theorem to evaluate \( \displaystyle \oint_C (x y)\,dx + (x^{2})\,dy \), where C is the boundary of the rectangle \( \displaystyle [0, 3] \times [0, 2] \), counterclockwise.
Green's theorem: ∮ P dx + Q dy = ∬ (∂Q/∂x − ∂P/∂y) dA.
Reviewed
\[ \frac{d}{d x} x^{2} - \frac{\partial}{\partial y} x y = x \]
∂Q/∂x − ∂P/∂y.✓ Proved
\[ \int\limits_{0}^{2}\int\limits_{0}^{3} x\, dx\, dy = 9 \]
Integrate over the rectangle.✓ Proved
Answer \( 9 \)
✓ Nihil obstat Lines: 2 proved, 1 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify