Davies, Charles, 1798-1876 · New York and Chicago, A. S. Barnes and company · leaf 48
THEOREM XI. If a quadrilateral be inscribed in a circle, the sum of either tiroof its opposite angles is equal to two right angles. Let A BCD be any quadrilateral in-scribed in a circle ; then will the sum ofthe two opposite angles, A and C, or Band D, be equal to two right angles. u For, the angle… … 48 G E O M E T R Y . Of the Ci re! and the angle C is measured by half the arc DAB, which subtends it. Hence, the sum of the two angles, A and C is measured by half the entire circumference. I\ But half the entire circumference is the n measure of two%right angles; therefore, th? sum of the…
Geometry · Plane trigonometry
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