Illustration used to prove the theorem "Two parallelograms are equal if two sides and the included angle…

Illustration of a two equal parallelograms. Two parallelograms are equal, if two sides and the included…

Diagram used to prove the theorem: "The opposite faces of a parallelopiped are equal and parallel."

Diagram used to prove the theorem: "The rectangular parallelopipeds which have two dimensions in common…

Diagram used to prove the theorem: "The rectangular parallelopipeds are to each other as the product…

Illustration of a two polygons. Polygons may be mutually equiangular without being mutually equilateral.

Illustration of two polygons. Polygons may be mutually equilateral without being mutually equiangular…

"Get a lamp-chimney, preferably cylindrical. With a diamond or a steel glass-cutter, cut a disk of window…

Illustration of 4 congruent rectangular prisms placed in the shape of a square. They are arranged to…

Diagram used to prove the theorem: "Two prisms are equal when the three faces about a trihedral of one…

Two triangular pyramids having equivalent bases and equal altitudes are equivalent.

Illustration to show that if the diagonals of a parallelogram are equal, the figure is a rectangle.

"Suppose a, b, to be a marble floor, and c, to be an ivory ball, which has be thrown towards the floor…

Five students are learning how to use scales to measure a book. They have balanced the book with some…

Illustration of a how to construct a square equivalent to the sum of two given squares.

Illustration of a how to construct a square equivalent to the difference of two given squares.

Illustration showing an equiangular triangle (one that has all three angles that are equal).

Illustration showing a triangle with exterior angles. This can be used to show the sum of the three…

Illustration showing an isosceles triangle with a segment inside. This can be used to show that in an…

Illustration showing two equal triangles. This can be used to show that two triangles are equal if the…

Illustration to show if two triangles have two sides of the one equal, respectively, to two sides of…

Illustration showing two equal right triangles. This can be used to show that two right triangles are…

Diagram used to prove the theorem: "The plane passed through two diagonally opposite edges of a parallelopiped…

Diagram used to prove the theorem: "Two triangular pyramids having equivalent bases and equal altitudes…

"Therefore, the small quantity in the spout balances the large quantity in the pot, or presses with…

"...represents two wave systems of equal periods and amplitudes but of opposite phases." -Avery 1895