Page 3 - Activity

Observation

1. area of ∆ABC = area of 36 smaller ∆’s
2. area of ∆PQR = area of 9 smaller ∆’s
3.

4.
2
= [9 smaller Δ’s/36 smaller Δ’s = = (1/2)
(because ΔABC ∼ ΔPQR)

Result
Thus it is verified that the ratio of the areas of two similar triangles is equal to the ratio of
the square of their corresponding sides.

Learning Outcome
Concept of area theorem is clear to the students through this activity.

Viva Voce

Question 1.
What are the criteria for two triangles to be similar ?
Answer:
Two triangles are said to be similar, if

 their corresponding angles are equal.
 their corresponding sides are in proportion

Question 2.
∆ABC ~ ∆DEF and their areas are respectively 64 cm and 121 cm . If EF = 15.4 cm,
2
2
then findBC.
Answer:
11.2 cm

Question 3.
Is it true, if the areas of two similar triangles are equal, then they are congruent ?
Answer:
Yes

Question 4.
What is the ratio of the area of an equilateral triangle described on one side of a square
to the area of an equilateral triangle described on one of its diagonal ?
Answer:
1:2