Ex.6.2 Q1 Triangles Solution - NCERT Maths Class 10

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In Figure, (i) and (ii), \(DE || BC.\) Find \(EC\) in (i) and \(AD\) in (ii)

 Video Solution
Ex 6.2 | Question 1

Text Solution


As we all know the Basic Proportionality Theorem (B.P.T) or (Thales Theorem)

Two triangles are similar if :

(i) Their corresponding angles are equal

(ii) Their corresponding sides are in the same ratio (or proportion)


(i) In\(\,\,\Delta ABC\) 

\[\begin{align} BC||DE \\ \end{align}\]

In\(\begin{align}\Delta ABC\,\,&\And \,\,\Delta ADE \end{align}\)

\[\begin{align} & \angle ABC=\angle ADE \\ & \left( \because \text{Corresponding}\,\text{angles} \right) \\\\ & \angle ACB=\angle AED \\ & \left( \because \text{Corresponding}\,\text{angles} \right) \\\\ &\quad \;\;\angle A=\angle A \\ &\text{(Common)} \\\\ & \Rightarrow \Delta ABC \sim \Delta \text{ADE} \\ \end{align}\]

\[\begin{align} \frac{AD}{DB}&=\frac{AE}{EC} \\  \frac{1.5}{3}&=\frac{1}{EC} \\ EC&=\frac{3\times 1}{1.5} \\  EC&=2\,\text{cm}\end{align}\]

(ii) Similarly, \(\Delta ABC \sim \Delta ADE\)

\[\begin{align} \frac{AD}{DB}&=\frac{AE}{EC} \\ \frac{AD}{7.2} &=\frac{1.8}{5.4} \\ AD&=\frac{7.2\times 1.8}{5.4} \\ AD&=2.4\,\text{cm} \\\end{align}\]

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