### Practical Geometry - Revision Notes

CBSE Class–VII Subject Mathematics

Revision Notes

Chapter –10

Practical Geometry

Revision Notes

Chapter –10

Practical Geometry

In this Chapter, we looked into the methods of some ruler and compasses constructions.- Given a line l and a point not on it, we used the idea of ‘equal alternate angles’ in a transversal diagram to draw a line parallel to l.
- We could also have used the idea of ‘equal corresponding angles’ to do the construction.
- Construction of Parallel Lines: Draw a line segment
*l*and mark a point A not lying on it. - Take any point B on
*l*and join B to A. - With B as centre and convenient radius, draw an arc cutting
*l*at C and AB and D. - Now with A as centre and the same radius as in above step draw an arc EF cutting AB at G.
- Place the metal point of the compasses at C and adjust the opening so that the pencil point is at D.
- With the same opening as in above step and with G as centre draw another arc cutting the arc EF and H.
- Now join AH and draw a line m.
- We studied the method of drawing a triangle, using indirectly the concept of congruence of triangles.

The following cases were discussed:

(i) SSS: Given the three side lengths of a triangle.

(ii) SAS: Given the lengths of any two sides and the measure of the angle between these sides.

(iii) ASA: Given the measures of two angles and the length of side included between them.

(iv) RHS: Given the length of hypotenuse of a right-angled triangle and the length of one of its legs.