This paper applies the Unitary Reference Principle (URP), first proposed in Brogley (2026a), extended to division in Brogley (2026b), and applied to the Riemann Hypothesis in Brogley (2026c), to the domain of geometry. The central claim is that every geometric measurement is a fraction of a declared reference R — and that this reframing unifies dozens of separately memorized geometric formulas into a single structural framework. Seven foundational claims are developed. First: all angles are fractions of one full rotation, declared as R = 1 complete rotation (360° or 2π radians). Every angular relationship — complementary, supplementary, the triangle angle sum, the polygon interior angle formula — follows structurally from this single declaration, requiring no separate memorization. Second: arc length, sector area, and central angle are all the same fractional statement about the same declared reference, revealing that three conventional formulas are one URP expression. Third: π is not a number greater than 1 but a bridge reference connecting the diameter domain to the circumference domain of the same circle. Fourth: area and volume are compound declared references computed in Step 0 (R = product of declared dimensions), with every sub-measurement expressed as a fraction of R. Fifth: trigonometric functions are already URP fractions — sin(θ) = opposite/hypotenuse = n/R where R is the declared hypotenuse — and the Pythagorean theorem is a Step 2 verification that the declared reference is preserved. Sixth: the Dehn invariant and Hilbert's Third Problem are reframed as URP angle-reference constraints; full treatment in companion paper (URP Series Paper 14, forthcoming). Seventh: the URP framework extends naturally to n-dimensional geometry, with implications for hyperbolic geometry, spherical geometry, and the quantum geometry of curved spacetime. Contents: Chapter 1: The Problem With Geometric Formulas | Chapter 2: Angles | Chapter 3: Circles, π, and the Bridge Reference | Chapter 4: Area and Volume | Chapter 5: Trigonometry | Chapter 6: Hilbert's Third Problem and the Dehn Invariant | Chapter 7: Higher Dimensions | Chapter 8: Open Problems and Conclusion Part of the URP Series: Paper 1 (Foundation): https://doi.org/10.5281/zenodo.19697119 Paper 2 (Division): https://doi.org/10.5281/zenodo.19733441 Paper 3 (Riemann Hypothesis): https://doi.org/10.5281/zenodo.19735713 Keywords geometry, Unitary Reference Principle, angles, area, volume, π, trigonometry, Pythagorean theorem, Dehn invariant, scissors congruence, Hilbert's Third Problem, aperiodic tiling, higher dimensions, n-dimensional geometry, declared reference, Step 0
Joshua Brogley (Tue,) studied this question.