We have learnt about the many shapes and diagrams, which were necessary to prove a theorem or solving exercises.
Normally, all these instruments are needed in drawing a geometrical figure, such as a triangle, a circle, a quadrilateral, a polygon, etc. with given measurements. But a geometrical construction is the process of drawing a geometrical figure using only two instruments — an ungraduated ruler, also called a straight edge and a compass. In construction where measurements are also required, you may use a graduated scale and protractor also.
Here you will have learnt how to construct a circle, the perpendicular bisector of a line segment, angles of 30°, 45°, 60°, 90° and 120°, and the bisector of a given angle, without giving any justification for these constructions.
Construction 11.1 : To construct the bisector of a given angle.
Construction 11.2 : To construct the perpendicular bisector of a given line segment.
Construction 11.3 : To construct an angle of 60° at the initial point of a given ray.
As some constructions of triangles will be done by using the constructions given in earlier classes. You may have noted that at least three parts of a triangle have to be given for constructing it but not all combinations of three parts are sufficient for the purpose.
Construction 11.4 : To construct a triangle, given its base, a base angle and sum of other two sides.
Construction 11.5 : To construct a triangle given its base, a base angle and the difference of the other two sides.
Construction 11.6 : To construct a triangle, given its perimeter and its two base angles.