Question taken from RD sharma

Class 10th

Chapter no. 4

Chapter name:- Triangles

Exercise :- 4.2

This is very basic and important questions.

In this question we have a triangle ΔABC,

In which D and E are points on the sides AB and AC respectively such that DE || BC.

It is also given that AD = 4 cm, AE = 8 cm, DB = x – 4 cm and EC = 3x – 19,

Now we have to find x.

Understanding and learning CBSE maths

RD sharma, DHANPAT RAI publication

Given:Length of side AD = 4 cm, AE = 8 cm, DB = x – 4 and EC = 3x – 19

To Find: length of side x.By using Thales Theorem, we get,

AD/BD = AE/CE – equation 1

Now, putting values in equation 1,

4/ (x – 4) = 8/ (3x – 19)

4(3x – 19) = 8(x – 4)

12x – 76 = 8(x – 4)

12x – 8x = – 32 + 76

4x = 44 cm

x = 11 cm

Therefore, Length of side x is 11 cm