This section is from the book "The Corner Cupboard; Or, Facts For Everybody", by Robert Kemp Philp. Also available from Amazon: The Corner Cupboard; or Facts for Everybody.

**Triangle**. A figure having three sides and three angles, called right-angled, when two of the sides are perpendicular to each other, and oblique-angled, when not so. The three angles are equal to two right angles, the sides are proportionate to their opposite angles, and the sides of different triangles having equal angles are proportionate to each other. These principles are the foundations of trigonometry, and of much mathematical science, because all figures may be reduced to triangles; and it hence appears that every figure contains twice as in my right angles less by four as it has sides, as 3 x 2 = 6 - 4 = 2, for a triangle ; or 7 x 2= 14, - 4, or 10 right angles for an heptagon.

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