Give a definition for each of the following terms. Are there other terms that need to be defined first? What are they, and how might you define them?

(i) Parallel lines

(ii) Perpendicular lines

(iii) Line segment

(iv) Radius of a circle

(v) Square

Yes, there are other terms that are needed to be defined first which are:

Plane: A plane is a flat surface on which geometric figures are drawn.

Point: A point is a dimensionless dot which is drawn on a plane surface.

Line: A line is collection of n number of points which can extend in both the directions and has only length or breadth.

Now,

(i) Parallel lines: When two or more lines do not intersect each other in a plane and perpendicular distance between them ramains constant then they are said to be parallel lines.

(ii) Perpendicular lines: When two lines intersect each other making a right angle in a plane then they are said to be perpendicular to each other.

(iii) Line segment: A line segment is a part of a line with two end points and cannot be extended further. It has a definite length or breadth.

(iv) Radius of circle: The fixed distance between the centre and the circumference of the circle is called radius of the circle.

(v) Square: A square is a quadrilateral in which all the four sides are equal and each internal angle is a right angle.