Chapter 6 Triangles NCERT Exemplar Solutions Exercise 6.2 Class 10 Maths
Chapter Name  NCERT Maths Exemplar Solutions for Chapter 6 Triangles Exercise 6.2 
Book Name  NCERT Exemplar for Class 10 Maths 
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Related Study  NCERT Solutions for Class 10 Maths 
Exercise 6.2 Solutions
Short Answer Questions with Reasoning
1. Is the triangle with sides 25 cm, 5 cm and 24 cm a right triangle? Give reason for your answer.
Solution
It is not true.
Taking,
a = 25 cm,
b = 5 cm and
c = 24 cm
Now,
b^{2} + c^{2} = (5)^{2} + (24)^{2}= 25 + 576 = 601
≠ (25)^{2}
Therefore, given sides do not make a right triangle because it does not satisfy the property of Pythagoras theorem.
2. It is given that Î”DEF ~ Î”RPQ. Is it true to say that ∠D = ∠R and ∠F = ∠P? Why?
Solution
It is not true
We know that, if two triangles are similar, then their corresponding angles are equal.
∠D = ∠R,
∠E = ∠P and
∠F = Q
3. A and B are respectively the points on the sides PQ and PR of a Î”PQR such that PQ = 12.5 cm, PA = 5 cm, BR = 6 cm and PB = 4 cm. Is AB  QR?
Give reason for your answer.
Solution
It is correct.
Given,
PQ = 12.5 cm,
PA = 5 cm,
BR = 6 cm and
PB = 4 cm
Also,
PB/BR = 4/6 = 2/3
So, QA = QP  PA
= 12.5  5 = 7.5 cm
PA/AQ = 5/7.5
= 2/3
So by converse of basic proportionality theorem, AB  QR.
4. In figure, BD and CE intersect each other at the point P. Is Î”PBC ~ Î”PDE? Why?
Solution
It is correct.
In Î”PBC and Î”PDE,
∠BPC = ∠EPD [vertically opposite angles]
PB/PD = 5/10 = 1/2
PC/PE = 6/12 = 1/2
So,
PB/PD = PC/PE
As, one angle of ∆PBC is equal to one angle of ∆PDE and the sides including these angles are proportional, so both triangles are similar.
So, ∆PBC ~ ∆PDE, by SAS similarity criterion.
5. In ∆PQR and ∆MST, ∠P = 55°, ∠Q =25°, ∠M = 100° and ∠S = 25°. Is Î”QPR ~ Î”TSM? Why?
Solution
It is not true.
As, the sum of three angles of a triangle is 180° .
In ∆PQR,
∠P + ∠Q + ∠R = 180°
⇒ 55° + 25° + ∠R = 180°
⇒ ∠R = 180°  (55° + 25°)
⇒ ∠R = 180°  80° = 100°
In ∆TSM,
∠T + ∠S + ∠M = 180°
⇒ ∠T + ∠25° + 100° = 180°
⇒ ∠T = 180° – (25° + 100°)
⇒ ∠T= 180° – 125°
⇒ ∠T= 55°
So,
In ∆PQR and ∆TSM,
∠P = ∠T,
∠Q = ∠S and
∠R = ∠M
∠PQR = ∠TSM [As, all corresponding angles are equal]
Therefore,
∆QPR is not similar to ∆TSM, because correct correspondence is P ↔ T, Q ↔ S and R ↔ M.
6. Is the following statement true? Why?
“Two quadrilaterals are similar, if their corresponding angles are equal”.
Solution
It is not true.
Two quadrilaterals are similar if their corresponding angles are equal and corresponding sides must also be proportional.
7. Two sides and the perimeter of one triangle are respectively three times the corresponding sides and the perimeter of the other triangle. Are the two triangles similar? Why?
Solution
Yes, It is true.
The corresponding two sides and the perimeters of two triangles are proportional, then the third side of both triangles will also in proportion.
8. If in two right triangles, one of the acute angles of one triangle is equal to an acute angle of the other triangle, can you say that the two triangles will be similar? Why?
Solution
It is false.
Let two right angled triangles be ∆ABC and ∆PQR
Where,
∠A = ∠P = 90° and
∠B = ∠Q = acute angle (Given)
So, by AA similarity criterion, ∆ABC ~ ∆PQR
9. The ratio of the corresponding altitudes of two similar triangles is 3/5. Is it correct to say that ratio of their areas is 6/5 ? Why ?
Solution
It is false.
Ratio of corresponding altitudes of two triangles having areas A1 and A2 respectively is 3/5. Using the property of area of two similar triangles,
So, the given statement is not correct.
10. D is a point on side QR of ∆PQR such that PD ⊥ QR. Will it be correct to say that ∆PQD ～∆RPD ? Why ?
Solution
No, it is false statement.
In given ∆PQD and ∆RPD,
PD = PD [common side]
∠PDQ = ∠PDR [each 90°]
Also, no other sides or angles are equal, so we can say that ∆PQD is not similar to ∆RPD.
But if ∠P = 90° , then
∠DPQ = ∠PRD
[each equal to 90°  ∠Q and by ASA similarity criterion, ∆PQD ～∆RPD]
11. In Fig. 6.5, if ∠D = ∠C, then is it true that ∆ADE ～∆ACB ? Why ?
Solution
True
In ∆ADE and ∆ACB,
∠A = ∠A [common angle]
∠D = ∠C [given]
∆ADE ~ ∆ACB [using AA similarity criterion]
12. Is it true to say that if in two triangles, an angle of one triangle is equal to an angle of another triangle and two sides of one triangle are proportional to the two sides of the other triangle, then the triangles are similar? Give reasons for your answer.
Solution
False
As, according to SAS similarity criterion, if one angle of a triangle is equal to an angle of the other triangle and the sides including these angles are proportional, then the two triangles are similar.
In the above question, one angle and two sides of two triangles are equal but these sides does not includes equal angle, so given statement is not true.