...additional axioms above proposed, articles 27, 32, 58, 59, and 69 become unnecessary. Theorem 178 is, The area of a trapezoid is equal to the product of its altitude by half the sum of its parallel sides. The labored demonstration here given is unnecessary. The truth...

...bh, § 333 and area A, 4 DC = J b'k. 4. /. area trapezoid ABCD = 1 h(b + l>(). Ax. 2 336. COROLLARY. The area of a trapezoid is equal to the product of its altitude and mid-line. § 219 EXERCISES D b C 1. From § 321 derive a proof .for the above theorem by means...