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5 questions · self-marked practice — reveal the answer and mark yourself.

Question 13 Marks
If the base of an isosceles triangle is produced on both sides, prove that the exterior angles so formed are equal to each other.
Answer
ED is a straight line segment and B and C an points on it.$\angle\text{EBC}=\angle\text{BCD}=\text{straight angle}=180^\circ$
$\angle\text{EBA}+\angle\text{ABC}=\angle\text{ACB}+\angle\text{ACD}$
$\angle\text{EBA}+\angle\text{ACD}+\angle\text{ACB}-\angle\text{ABC}$
$\angle\text{EBA}=\angle\text{ACD}$ [From (i) ABC = ACD]
$\angle\text{ABE}=\angle\text{ACD}$
Hence proved.
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Question 23 Marks
In two triangles ABC and ADC, if AB = AD and BC = CD. Are they congruent?
Answer
The given information and corresponding figure is given below
AB = AD
BC = CD

From the figure, we have
AB = AD (given)
BC = CD (given)
And,
AC = AC (common sides)
Hence, triangles ABC and ADC are congruent to each other.
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Question 43 Marks
In Fig. $\text{AD}\perp\text{CD}$ and $\text{CB}\perp\text{CD}.$ If $\text{AQ}=\text{BP}$ and $\text{DP}=\text{CQ},$ prove that $\angle\text{DAQ}=\angle\text{CBP}.$
Answer
In $\triangle\text{DAQ}$ and $\triangle\text{CBP}$$\angle\text{ADQ}=\angle\text{BCP}=90^\circ$
$\text{DP}=\text{CQ}$ [given]
$\Rightarrow\text{DP}+\text{PQ}=\text{CQ}+\text{PQ}$
$\Rightarrow\text{DQ}=\text{CP}$
$\text{AQ}=\text{BP}$ [given]
By RHS congurence criterion $\triangle\text{DAQ}\cong\triangle\text{CBP}$$\therefore\angle\text{DAQ}=\angle\text{CBP}$ [c.p.c.t]
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Question 53 Marks
If ABC and DEF are two triangles such that AC = 2.5cm, BC = 5cm, $\angle\text{C}=75^\circ,$ DE = 2.5cm DF = 5cm and $\angle\text{D}=75^\circ.$ Are two triangles congruent?
Answer
It is given that $\text{AC}=2.5$
$\text{BC}=5$
$\angle\text{C}=75^\circ$
$\text{DE}=2.5$
$\text{DF}=5$
$\angle\text{D}=75^\circ$
Since, two sides and angle between them are equal, therefore triangle ABC and DEF are congruent.
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