remove abs() from trapezoidal rule segment sum

[HrachShah]

The trapezoidal_area function in maths/area_under_curve.py wraps the per-segment trapezoid sum in abs(...), which forces the running total to be non-negative.

The trapezoidal rule is a signed-area approximation: each linear segment between (x1, f(x1)) and (x2, f(x2)) contributes (f(x1) + f(x2)) * (x2 - x1) / 2 to the running total. The previous code wrapped that in abs(), which forced the running total to be non-negative. For functions that are positive in the test range the abs() was a no-op and the existing doctests passed, but two natural cases broke:

• f(x) = -x**2 from -1.0 to 1.0 returned +0.6666... instead of -0.6666...
• f(x) = x from -2.0 to 2.0 returned 4.0 instead of 0 (the symmetric linear function integrates to zero across the origin)

The doctests use f(x)=5 and f(x)=9*x**2 — both non-negative in the test range, so they coincidentally worked. Drop the abs() and the formula returns the correct signed approximation for any real-valued f.

Verified with python3 -m doctest maths/area_under_curve.py: 5/5 still pass.

Summary by Sourcery

Bug Fixes:

• Fix trapezoidal integration so that functions with negative values or symmetric positive/negative regions produce the correct signed area instead of an always non-negative result.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adjusts the trapezoidal integration implementation to compute true signed area by removing an absolute value operation from the per-segment contribution formula, preserving existing doctests.

File-Level Changes

Change	Details	Files
Compute signed trapezoidal area contributions instead of forcing them non-negative.	Remove abs() around the per-segment trapezoidal area increment so each segment can contribute positive or negative signed area Keep loop structure, step calculation, and function evaluations unchanged to preserve behavior apart from sign handling	maths/area_under_curve.py

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