 ### 2 Equal Parallelograms

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

Illustration of a two equal parallelograms. Two parallelograms are equal, if two sides and the included… ### Equal and Parallel Opposite Faces of a Parallelopiped

Diagram used to prove the theorem: "The opposite faces of a parallelopiped are equal and parallel." ### Relationship Between 2 Parallelopipeds With Equal Altitudes

Diagram used to prove the theorem: "The rectangular parallelopipeds which have two dimensions in common… ### Relationship Between Dimensions of Parallelopipeds

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

Illustration showing two congruent pentagons. ### Equiangular Polygons

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

Illustration of two polygons. Polygons may be mutually equilateral without being mutually equiangular… ### Water Pressure Experiment

"Get a lamp-chimney, preferably cylindrical. With a diamond or a steel glass-cutter, cut a disk of window… ### 4 Congruent Rectangular Prisms

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

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

Two triangular pyramids having equivalent bases and equal altitudes are equivalent. ### Rectangle With Diagonals

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

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

"Angle of incidence equals angle of reflection." —Croft 1917 ### Children Using Scales

Five students are learning how to use scales to measure a book. They have balanced the book with some… ### Square Constructed to be Equal to the Sum of Two Given Squares

Illustration of a how to construct a square equivalent to the sum of two given squares. ### Square Constructed to be Equal to the Difference of Two Given Squares

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

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

"Having equal sides." — Williams, 1889 ### Triangle with Exterior Angles Drawn

Illustration showing a triangle with exterior angles. This can be used to show the sum of the three… ### Isosceles Triangle degrees 60, 60, 60

An isosceles triangle with angles 60, 60, 60 ### Isosceles Triangle With Interior Segment Drawn

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

Illustration showing two equal triangles. ### Equal Triangles by Side Side Side

Illustration showing two equal triangles. This can be used to show that two triangles are equal if the… ### Proof of Equal Triangles Drawing

Illustration to show if two triangles have two sides of the one equal, respectively, to two sides of… ### Equal Right Triangles by Hypotenuse Leg

Illustration showing two equal right triangles. This can be used to show that two right triangles are… ### Parallelopiped Divided Into Triangular Prisms

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

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

"Therefore, the small quantity in the spout balances the large quantity in the pot, or presses with… ### Waves with Equal Periods and Opposite Amplitudes

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