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KC Sinha Mathematics Solution Class 9 Chapter 9 Triangles exercise 9.2

Page 9.38

EXERCISE 9.2


Type 1

 


QUESTION 1

Fill up the blanks so that the statements given below are true :

(i) In a triangle, ,difference of any two sides is __ than the third side

(ii) In a triangle, sum of any two sides is ___ than the third side

(iii) In a triangle, side opposite to larger angle is ___

(iv) In a triangle, side opposite to the smallest angle is __

(v) In a triangle, angle Opposite to the greatest side is __

(vi) Of all the line segments that can be drawn to a given line from a point not lying on it, the smallest is ___

(vii) In a right angled triangle, hypotenuse is the ___ side

(viii) Perimeter of a triangle is ___  than sum of its three medians.

(ix) The sum of three altitudes of a triangle is __ than its perimeter

(x) In a ΔABC , if ∠B=120° , then side opposite to ∠B will be __

Sol :

 


QUESTION 2

Which of the following statements are true (T) and which are false (F) :

(i) Of all the line segments that can be drawn to a given line from a point not lying on it, perpendicular line segment is the shortest one.

(ii) In a triangle, sum of two sides is smaller than the third side.

(iii) In a triangle,sum of two angles is greater than the third angle.

(iv) In an acute angled triangle, sum of two angles is greater than the third angle.

(v) In a triangle, difference of two sides is equal to the third side.

(vi) In a triangle. sum of two sides is greater than the third side.

Sol :

 


QUESTION 3

See f‌igure below and fill up the blanks with the signs of inequality and equality.

(i) ∠BDA __ ∠DCB

(ii) ∠BDA __ ∠DBC

(iii) If ∠ABC>∠ACB, then AC__AB

(iv) If ∠ABC=∠ACB, then AC__AB

(v) If ∠ABD=∠ADB, then AB__AD

Sol :

 


QUESTION 4

(i) In a triangle, two sides are 5cm and 3cm , then can third side be 1.5 cm ?

(ii) If AB=4 cm, BC=3 cm and CA=8 cm, then is construction of ΔABC possible ?

(iii) In a ΔABC , if ∠A=60° , ∠B=75° and ∠C=45° , then write,

(a) Greatest side (b) Smallest side

(iv) Of all the line segments that can be drawn to a line from a point outside the line which is the smallest line segment ?

(v) How many perpendiculars can be drawn on a line from a point outside the line ?

Sol :

 


QUESTION 5

In an examination. there was a question: construct a triangle whose three sides are of length 3.6 cm, 4.6 cm and 8.4 cm respectively. Was the question correct ? Explain giving reasons.

Sol :

 


QUESTION 6

Can a ΔABC be constructed, if AB=6cm , BC=4cm and CA=3.2cm ? Given reasons.

Sol :


TYPE 2


QUESTION 7

What can be the values in integer, of the third side of a triangle, if its two sides are as follows ?

(a) 2 and 6

(b) 7 and 7

(c) 4 and 8

(d) 3 and 9

Sol :

 


TYPE 3

 


QUESTION 8

In figure below, sides PQ and PR are produced and ∠SQR<∠TRQ . Show that PR>PQ

Sol :

 


QUESTION 9

In figure below, AB>AC and D is a point on BC. Show that AB>AD

Sol :

 


QUESTION 10

In figure below, PR>PQ and PS is a bisector of ∠P . Show that x>y


Sol :

 


QUESTION 11

In triangle (Fig. below) , ∠B<∠A and ∠C<∠D , then prove that AD<BC.


Sol :

 


QUESTION 12

Prove that the sum of any two sides of a triangle is greater than twice the median of the third side.

 

<fig to be added>

Sol :

 


QUESTION 13

Prove that , sum of three sides of a triangle is greater than the sum of its medians.

Sol :

 


QUESTION 14

In the adjoining figure, from point P not lying on a line m , line segments are drawn to m , PD being the shortest one. If B and C be the points on m such that D is the mid point of BC . Prove that PB=PC

[Hint: Let m be a line and P be a point not lying on m. On the line m , B and C are two points such that BD=DC.

To prove : PB=PC

Proof: Of line segments drawn from P to m. PD is the smallest,

∴PD⊥m

That is , ∠PDB=∠PDC=90°

Now, prove congruence of ΔPBD and ΔPCD ]


Sol :

 


QUESTION 15

In a ΔABC, internal bisectors of ∠B and ∠C meet at point O. If AC>AB, then prove that OC>OB.

[Hint: AC>AB

⇒∠ABC>∠ACB

⇒1/2∠ABC>1/2∠ACB

⇒∠OBC>∠OCB

⇒∠OC<∠OB]


Sol :

 


QUESTION 16

Prove that the sum of distances of vertices of a triangle from any point inside the triangle is greater than its half perimeter.

Sol :

 


QUESTION 17

In adjoining f‌igure, AP⊥l and and PR>PQ, prove that AR>AQ

[Hint: Take PQ=PS and join AS

∠1=∠3>∠2

∠1>∠2

AR>AQ]


Sol :

 


QUESTION 18

S is any point in the interior of ΔPQR, show that 

SQ+SR<PQ+PR

[Hint: Join QS and produce this to cut PR at T]


Sol :

 


QUESTION 19

In ΔPQR, S is a point on the side QR. Show that PQ+QR+RP>2PS


Sol :

 


QUESTION 20

O is a point inside a quadrilateral ABCD which is not at the point of intersection of diagonals . Prove that

OA+OB+OC+OD>AC+BC

Sol :

 


QUESTION 21

In figure , AB=AC , then prove that AF>AE

[Hint: AB=AC

⇒From ΔEBD, ∠4>∠2

⇒∠4>∠3 [AB=AC, ∠2=∠3]

⇒∠4>∠5

⇒In ΔAEF; AF>AE

]

<fig to be added>

Sol :

 


QUESTION 22

In figure below, T is a point on the side QR of ΔPQR, S is a point such that RT=ST. Prove that PQ+PR>QS


Sol :

 


QUESTION 23

In the f‌igure below, AC>AB and D is a point on AC such that AB=AD. Prove that CD<BC

<fig to be added>

[Hint: AB=AD

In ΔABC, AB+BC>AC

AB+BC>AD+CD

BC>CD

CD<BC [AB=AD]

]

Sol :

 


 

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