Home›Calculus 2›Area in polar coordinates›Problem 8.26

Area in polar coordinates

Problem 8.26 · easy

Find the area of the region inside \( \displaystyle r = 5 \sin{\left(\theta \right)} \).

Area in polar coordinates is ½∫ r² dθ over the angles that trace the region once.
Reviewed
Here θ runs from 0 to pi.
Reviewed
\[ \int\limits_{0}^{\pi} \frac{25 \sin^{2}{\left(\theta \right)}}{2}\, d\theta = \frac{25 \pi}{4} \]
Integrate.✓ Proved

Answer \( \frac{25 \pi}{4} \)

✓ Nihil obstat Lines: 1 proved, 2 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. How we verify

The full receipt

Line	Status	Checked by	Detail
1	Reviewed	reviewers: gpt-oss:20b, qwen3.6:27b-mlx	a sentence; read, not computed
2	Reviewed	reviewers: gpt-oss:20b, qwen3.6:27b-mlx	a sentence; read, not computed
3	✓ Proved	sympy 1.14.0	simplify(lhs - rhs) reduced to 0
answer, a second way	✓ Checked independently	sympy 1.14.0 + mpmath 1.3.0	the shoelace formula on 20,000 points of the curve gives the same area

Reviewers

gpt-oss:20b: pass
qwen3.6:27b-mlx: pass — The solution correctly identifies the curve as a circle of diameter 5 traced once as theta ranges from 0 to pi, and the integration is correct.

Every verdict on record (6)

qwen3.6:27b-mlx: pass 2026-09-28 — The solution correctly identifies the curve as a circle of diameter 5 traced once as theta ranges from 0 to pi, and the integration is correct.
gpt-oss:20b: pass 2026-09-28
qwen3.6:27b-mlx: pass 2026-09-27 — The solution correctly identifies the bounds for a single traversal of the circle r = 5 sin(theta) and applies the polar area formula accurately.
gpt-oss:20b: pass 2026-09-27
qwen3.6:27b-mlx: pass 2026-09-26 — The solution correctly identifies the curve as a circle traced once over [0, pi] and applies the polar area formula accurately.
gpt-oss:20b: pass 2026-09-26

Proved: SymPy reduced the difference between the two sides to zero. Checked independently: a separate method, named above, confirmed it. Checked numerically: the two sides agree at every sampled point, which is evidence, not proof. Reviewed: a model or a person read it; that is all a sentence can have. Solution by generator:structured/polar_area, checked 2026-09-28 with SymPy 1.14.0.