Geometrical Constructions
Procedure
1. Divide a straight line into a given number of equal parts.
- Draw a line with the given length and mark it as AB.
- Draw a line AC at any suitable angle.
- Using a divider, cut off equal number of parts of the same length on the line AC.
- Mark these points as 1’,2’,3’ and so on.
- Join the last point with the point B on the given line.
- Draw parallel lines from the rest of the points joining the line AB, dividing it into equal parts.
2. To inscribe a regular pentagon in a circle of a given diameter.
- With AB as the given diameter, construct a circle.
- Divide the diameter into 5 equal parts.
- Draw arcs from A and B, with AB as the radius and mark the point of their intersection as C.
- Join C with the second division on line AB and extend it to join the circle at D.
- Join A-D which is the side of the pentagon.
- From D mark an arc on the circumference of the circle with radius AD. Repeat the same to obtain points E, F and G
- Join the points D-E, E-F and F-G. The figure A-D-E-F-G so obtained is a regular pentagon.
3. To construct a regular hexagon with a given side.
- Draw the line with the given length and mark it as AB.
- Extend this line to P such that BP=AB.
- With B as the centre and AP as the diameter, draw a semicircle.
- Divide this semicircle into 6 equal parts.
- Draw a line from B joining the 2nd division. Mark the point as C.
- Join B with the 3rd, 4th and 5th divisions and extend them.
- Starting from the 2nd division, with radius AB, obtain an arc on B-3 and mark it as D.
- With the same radius, Mark off E on the line B-4.
- From E, mark F on the line B-5.
- The figure so obtained by joining A-B-C-D-E-F is a regular hexagon.
4. To draw in a given equilateral triangle, three equal circles, each touching the other two sides and the other two circles.
- Draw a side of an equilateral triangle with the given length. Name it AB.
- With AB as the radius, draw arcs from A and B. Mark their point of intersection as C.
- Join A-C and B-C.
- Bisects angle A and B and extend the lines such that they pass the midpoint on the opposite sides of the triangle.
- Drop a perpendicular from C, meeting these lines at their point of intersection O and extending it to the opposite side of the triangle. Mark it as P.
- Bisect the angle CPB and mark point M where it meets the angle bisector of B.
- Drop a perpendicular from M on the side of the triangle and name it as V.
- With M as the centre and MV as the radius, draw a circle touching the two sides of the triangle.
- Construct another circle with O as the centre and OM as the radius. Mark the points L and N where it cuts the other two lines.
- Draw circles from L and N having a radius MV, such that they touch the two sides of the triangle and the other two circles