Forms Small 320×71 Medium 640×143 Large 1024×229 Download Tiff Original 2400×536 | (131.5 KB) Description Showing different types of forms or shapes: rectangle, right triangle, acute triangle, and obtuse triangle. Keywords acute triangle, forms, geometry, obtuse triangle, rectangle, Right Triangle, shapes, types of triangles Galleries General Geometric Illustrations Source: Ellsworth D. Foster ed. The American Educator (vol. 3) (Chicago, IL: Ralph Durham Company, 1921) Courtesy the private collection of Roy Winkelman
