# Ex.6.2 Q1 Triangles Solution - NCERT Maths Class 10

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## Question

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

Video Solution
Triangles
Ex 6.2 | Question 1

## Text Solution

Reasoning:

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)

Steps:

(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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