Q20 of 20 Page 11

Let’s first construct ∆ABC with sides


Steps to draw ∆ABC


1. Draw base AB of side 6cm


2. With A as center, and 6cm as radius, C


Draw an arc


With B as center, and 10cm as radius,


Draw an arc.


3. Let C be the point where the two arc 8cm amd10cm


Intersect. Join AC & BC.


Thus, ∆ABC, is required triangle.


Now, let’s make similar triangle with scale factor = .



Steps of construction


1.Draw any ray AX making an acute angle with AB on the side opposite to the vertex C.



2. mark 5(the greater of 3 & 5 in ) points


On AX so that AA1 = A1A2 = A2A3…...and so on.



3.join A3B (3rd point is smaller in)And draw a line through A5 parallel to A3B, to intersect AB extended at B.



4.Draw a line through B to the line BC to intersect AC extended at C.



Thus, ∆AB'C' is the required triangle.


Justification


Since scale factor is ,


We need to prove



By construction



Also, BC is parallel to B’C


SO, they will make the same angle with AB


ABC = AB'C' (corresponding angles)…….(2)


Now, In ∆ABC & ∆AB’C’


A = A (common)


ABC = AB'C' (from 2)


∆ABC~∆AB'C' (AA Similarity)


Since, corresponding sides of similar triangle are in the same ratio



So,



Thus, our construction is justified.


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