Lab Manual: Verify that in a Triangle, Longer Side has the Greater Angle | Lab Manuals for Class 9 PDF Download

Objective

Materials Required
Cardboard, Coloured glazed papers, White paper, Tracing paper, Scissors, Geometry box, Sketch pens, Adhesive

Prerequisite Knowledge
Concept of triangle and its properties.

Procedure

• Take a cardboard of suitable size and by using adhesive, paste a white paper on it.
• Cut out a ΔABC from a glazed paper and by using adhesive, paste it on cardboard, (see Fig. 15.1)

• Measure the lengths of all the three sides of ΔABC and identify that which of them is longest.
• All the three angles of a triangle are to be marked, (see Fig. 15.2) 

• Using a tracing paper, make the cut out of the angle opposite to the longest side SC, i.e. ∠A. (see Fig. 15.3)

• Compare the cut out of the angle with remaining angles. (see Fig. 15.4)

Demonstration
We came to know that ∠A > ∠B and ∠A > ∠C , BC > AC, So, we get since ∠A > ∠B
Also, BC > AB, since ∠A > ∠C
Thus, we observe that the angle belongs to longer side is greater than the angle opposite to other side.

Observation

• Length of side AB = ……….. , Length of side BC = ………. , Length of side CA = ………… ,
• Measure of the angle opposite to the longest side = …………. ,
• Measure of the other two angles = …………… and ………. ,
• The angle opposite to the …………. side ……….. is than either of the other two angles.

Result
We have verified experimentally that in a triangle, the longest side has the greater angle opposite to it.

Application
The result can be useful in different geometrical problems.