8
IX-CLASS MATHEMATICS
EXERCISE - 3.1
1. Answer the following:
i.
How many dimensions a solid has?
ü.
How many books are there in Euclid's Elements ?
111.
Write the number of faces of cube and cuboid.
iv.
What is sum of interior angles of a triangle?
V.
Write three un-defined terms of geometry.
Answers
Answer:
(i) Polyhedrons, Curved Solids and Surface Area. This page examines the properties of three-dimensional or 'solid' shapes. A two-dimensional shape has length and width. A three-dimensional solid shape also has depth.
(ii) The thirteen books of Euclid's Elements.
(iii )A cube is a 3-D solid shape, which has 6 sides. Along with that, it has 8 vertices and 12 edges such that 3 edges meet at one vertex point. A cuboid is a polyhedron having six faces, eight vertices and twelve edges.
(iv) The formal proof that shows the measures of interior angles of a triangle sum to 180°.
(v) In geometry, formal definitions are formed using other defined words or terms. There are, however, three words in geometry that are not formally defined. These words are point, line and plane, and are referred to as the "three undefined terms of geometry". ... a point has no length, no width, and no height (thickness).