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Q5:
In Fig. 6.20, $DE \parallel OQ$ and $DF \parallel OR$. Show that $EF \parallel QR$.
In Fig. 6.20, $DE \parallel OQ$ and $DF \parallel OR$. Show that $EF \parallel QR$.
Solution :
Given: In $\triangle PQR$, we have points $D, E,$ and $F$ on sides $PQ, PR,$ and $QR$ respectively (based on the standard configuration of this theorem). Specifically, $DE \parallel OQ$ and $DF \parallel OR$, where $O$ is a point inside the triangle.
To Prove: $EF \parallel QR$.
Step 1: Applying Thales Theorem (Basic Proportionality Theorem) in $\triangle POQ$
We are given that $DE \parallel OQ$. According to the Basic Proportionality Theorem (BPT), if a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points, the other two sides are divided in the same ratio.
In $\triangle POQ$, since $DE \parallel OQ$:
$\frac{PD}{DQ} = \frac{PE}{EO}$ --- (Equation 1) [By Basic Proportionality Theorem]
Step 2: Applying Thales Theorem in $\triangle POR$
We are given that $DF \parallel OR$. Applying the Basic Proportionality Theorem in $\triangle POR$:
$\frac{PD}{DQ} = \frac{PF}{FR}$ --- (Equation 2) [By Basic Proportionality Theorem]
Step 3: Comparing the Equations
From Equation 1 and Equation 2, we observe that the left-hand side (LHS) of both equations is identical ($\frac{PD}{DQ}$). Therefore, we can equate the right-hand sides (RHS):
$\frac{PE}{EO} = \frac{PF}{FR}$ --- (Equation 3) [By Euclid's Axiom: Things which are equal to the same thing are equal to one another]
Step 4: Applying the Converse of the Basic Proportionality Theorem
In $\triangle PQR$, we have established that $\frac{PE}{EO} = \frac{PF}{FR}$.
According to the Converse of the Basic Proportionality Theorem, if a line divides any two sides of a triangle in the same ratio, then the line is parallel to the third side.
Since $\frac{PE}{EO} = \frac{PF}{FR}$ in $\triangle PQR$, it follows that the line segment $EF$ must be parallel to the base $QR$.
Therefore, $EF \parallel QR$.
Final Answer: Since the ratios of the segments on sides $PQ$ and $PR$ are equal, by the converse of the Basic Proportionality Theorem, $EF \parallel QR$.
More Questions from Class 10 Mathematics Triangles EXERCISE 6.2
- Q1(i): In Fig. 6.17, (i) and (ii), $DE \parallel BC$. Find $EC$ in (i).
- Q1(ii): In Fig. 6.17, (i) and (ii), $DE \parallel BC$. Find $AD$ in (ii).
- Q10: The diagonals of a quadrilateral $ABCD$ intersect each other at the point $O$ such that $\frac{AO}{BO} = \frac{CO}{DO}$. Show that $ABCD$ is a trapezium.
- Q2(i): $E$ and $F$ are points on the sides $PQ$ and $PR$ respectively of a $\triangle PQR$. For each of the following cases, state whether $EF \parallel QR$ : (i) $PE = 3.9$ cm, $EQ = 3$ cm, $PF = 3.6$ cm and $FR = 2.4$ cm
- Q2(ii): $E$ and $F$ are points on the sides $PQ$ and $PR$ respectively of a $\triangle PQR$. For each of the following cases, state whether $EF \parallel QR$ : (ii) $PE = 4$ cm, $QE = 4.5$ cm, $PF = 8$ cm and $RF = 9$ cm
- Q2(iii): $E$ and $F$ are points on the sides $PQ$ and $PR$ respectively of a $\triangle PQR$. For each of the following cases, state whether $EF \parallel QR$ : (iii) $PQ = 1.28$ cm, $PR = 2.56$ cm, $PE = 0.18$ cm and $PF = 0.36$ cm
- Q3: In Fig. 6.18, if $LM \parallel CB$ and $LN \parallel CD$, prove that $\frac{AM}{AB} = \frac{AN}{AD}$.
- Q4: In Fig. 6.19, $DE \parallel AC$ and $DF \parallel AE$. Prove that $\frac{BF}{FE} = \frac{BE}{EC}$.
- Q6: In Fig. 6.21, $A$, $B$ and $C$ are points on $OP$, $OQ$ and $OR$ respectively such that $AB \parallel PQ$ and $AC \parallel PR$. Show that $BC \parallel QR$.
- Q7: Using Theorem 6.1, prove that a line drawn through the mid-point of one side of a triangle parallel to another side bisects the third side. (Recall that you have proved it in Class IX).
- Q8: Using Theorem 6.2, prove that the line joining the mid-points of any two sides of a triangle is parallel to the third side. (Recall that you have done it in Class IX).
- Q9: $ABCD$ is a trapezium in which $AB \parallel DC$ and its diagonals intersect each other at the point $O$. Show that $\frac{AO}{BO} = \frac{CO}{DO}$.
CBSE Solutions for Class 10 Mathematics Triangles
Chapters in CBSE - Class 10 Mathematics
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