Area between curves
Problem 5.69 · medium
Find the area of the region bounded by \( \displaystyle y = - 2 x^{2} + 15 x - 21 \) and \( \displaystyle y = x + 3 \).
- \[ \left(8 - 2 x\right) \left(x - 3\right) = - 2 x^{2} + 14 x - 24 \]Set the curves equal: top − bottom, factored.✓ Proved
- They cross at x = 3 and x = 4; between them y = -2*x**2 + 15*x - 21 is on top.
- \[ \int\limits_{3}^{4} \left(- 2 x^{2} + 14 x - 24\right)\, dx = \frac{1}{3} \]Area = ∫ (top − bottom) dx.✓ Proved
Answer \( \frac{1}{3} \)
Lines: 2 proved, 1 not checked. The answer was also checked a second way, without looking at the solution. The explanation has not been reviewed yet.
The full receipt
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| 2 | Not checked | — | 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 | numerical quadrature of |top − bottom| gives the same area |
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/area_between_curves, checked 2026-09-26 with SymPy 1.14.0.