### 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