NCERT Solutions for Class 10 Maths Exercise 10.2

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NCERT solutions for Maths Circles Download as PDF

NCERT Solutions for Class 10 Maths Exercise 10.2

NCERT Solutions for Class 10 Maths Circles

In Q 1 to 3, choose the correct option and give justification.

1. From a point Q, the length of the tangent to a circle is 24 cm and the distance of Q from the centre is 25 cm. The radius of the circle is:

(A) 7 cm

(B) 12 cm

(C) 15 cm

(D) 24.5 cm

Ans. (A) OPQ =

[The tangent at any point of a circle is to the radius

through the point of contact]

In right triangle OPQ,

[By Pythagoras theorem]

= 625 – 576 = 49

OP = 7 cm


2. In figure, if TP and TQ are the two tangents to a circle with centre O so that POQ = then PTQ is equal to:

(A)

(B)

(C)

(D)

Ans. (B) POQ = , OPT = and OQT =

[The tangent at any point of a circle is to the radius through the point of contact]

In quadrilateral OPTQ,

POQ + OPT + OQT + PTQ =

[Angle sum property of quadrilateral]

+ PTQ =

+ PTQ =

PTQ =


3. If tangents PA and PB from a point P to a circle with centre O are inclined to each other at angle of , then POA is equal to:

(A)

(B)

(C)

(D)

Ans. (A) OPQ =

[The tangent at any point of a circle is to the radius

through the point of contact]

OPA = BPA

[Centre lies on the bisector of the

angle between the two tangents]

In OPA,

OAP + OPA + POA =

[Angle sum property of a triangle]

+ POA =

+ POA =

POA =


4. Prove that the tangents drawn at the ends of a diameter of a circle are parallel.

Ans. Given: PQ is a diameter of a circle with centre O.

The lines AB and CD are the tangents at P and Q respectively.

To Prove: AB CD

Proof: Since AB is a tangent to the circle at P and OP is the radius through the point of contact.

OPA = ……….(i)

[The tangent at any point of a circle is to the radius through the point of contact]

CD is a tangent to the circle at Q and OQ is the radius through the point of contact.

OQD = ……….(ii)

[The tangent at any point of a circle is to the radius through the point of contact]

From eq. (i) and (ii), OPA = OQD

But these form a pair of equal alternate angles also,

AB CD


5. Prove that the perpendicular at the point of contact to the tangent to a circle passes through the centre.

Ans. We know that the tangent at any point of a circle is perpendicular to the radius through the point of contact and the radius essentially passes through the centre of the circle, therefore the perpendicular at the point of contact to the tangent to a circle passes through the centre.


6. The length of a tangent from a point A at distance 5 cm from the centre of the circle is 4 cm. Find the radius of the circle.

Ans. We know that the tangent at any point of a circle is to the radius through the point of contact.

OPA =

[By Pythagoras theorem]

= 9

OP = 3 cm


7. Two concentric circles are of radii 5 cm and 3 cm. Find the length of the chord of the larger circle which touches the smaller circle.

Ans. Let O be the common centre of the two concentric circles.

Let AB be a chord of the larger circle which touches the smaller circle at P.

Join OP and OA.

Then, OPA =

[The tangent at any point of a circle is to the radius through the point of contact

OA2 = OP2 + AP2

[By Pythagoras theorem]

= 16

AP = 4 cm

Since the perpendicular from the centre of a circle to a chord bisects the chord, therefore

AP = BP = 4 cm

AB = AP + BP

= AP + AP = 2AP

= = 8 cm


8. A quadrilateral ABCD is drawn to circumscribe a circle (see figure). Prove that:

AB + CD = AD + BC

Ans. We know that the tangents from an external point to a circle are equal.

AP = AS ……….(i)

BP = BQ ……….(ii)

CR = CQ ……….(iii)

DR = DS……….(iv)

On adding eq. (i), (ii), (iii) and (iv), we get

(AP + BP) + (CR + DR)

= (AS + BQ) + (CQ + DS)

AB + CD = (AS + DS) + (BQ + CQ)

AB + CD = AD + BC


NCERT Solutions for Class 10 Maths Exercise 10.2

9. In figure, XY and X’Y’ are two parallel tangents to a circle with centre O and another tangent AB with point of contact C intersecting XY at A and X’Y’ at B. Prove that AOB =

Ans. Given: In figure, XY and X’Y’ are two parallel tangents to a circle with centre O and another

tangent AB with point of contact C intersecting XY at A and X’Y’ at B.

To Prove: AOB =

Construction: Join OC

Proof: OPA = ……….(i)

OCA = ……….(ii)

[Tangent at any point of a circle is to

the radius through the point of contact]

In right angled triangles OPA and OCA,

OA = OA [Common]

AP = AC [Tangents from an external

point to a circle are equal]

OPA OCA

[RHS congruence criterion]

OAP = OAC [By C.P.C.T.]

OAC = PAB ……….(iii)

Similarly, OBQ = OBC

OBC = QBA ……….(iv)

XY X’Y’ and a transversal AB intersects them.

PAB + QBA =

[Sum of the consecutive interior angles on the same side of the transversal is ]

PAB + QBA

= ……….(v)

OAC + OBC =

[From eq. (iii) & (iv)]

In AOB,

OAC + OBC + AOB =

[Angel sum property of a triangle]

+ AOB = [From eq. (v)]

AOB =

Hence proved.


NCERT Solutions for Class 10 Maths Exercise 10.2

10. Prove that the angel between the two tangents drawn from an external point to a circle is supplementary to the angle subtended by the line-segment joining the points of contact at the centre.

Ans. OPA = ……….(i)

OCA = ……….(ii)

[Tangent at any point of a circle is to

the radius through the point of contact]

OAPB is quadrilateral.

APB + AOB + OAP + OBP =

[Angle sum property of a quadrilateral]

APB + AOB + + =

[From eq. (i) & (ii)]

APB + AOB =

APB and AOB are supplementary.


NCERT Solutions for Class 10 Maths Exercise 10.2

11. Prove that the parallelogram circumscribing a circle is a rhombus.

Ans. Given: ABCD is a parallelogram circumscribing a circle.

To Prove: ABCD is a rhombus.

Proof: Since, the tangents from an external point to a circle are equal.

AP = AS ……….(i)

BP = BQ ……….(ii)

CR = CQ ……….(iii)

DR = DS……….(iv)

On adding eq. (i), (ii), (iii) and (iv), we get

(AP + BP) + (CR + DR)

= (AS + BQ) + (CQ + DS)

AB + CD = (AS + DS) + (BQ + CQ)

AB + CD = AD + BC

AB + AB = AD + AD

[Opposite sides of gm are equal]

2AB = 2AD

AB = AD

But AB = CD and AD = BC

[Opposite sides of gm]

AB = BC = CD = AD

Parallelogram ABCD is a rhombus.


NCERT Solutions for Class 10 Maths Exercise 10.2

12. A triangle ABC is drawn to circumscribe a circle of radius 4 cm such that the segments BD and DC into which BC is divided by the point of contact D are of lengths 8 cm and 6 cm respectively (see figure). Find the sides AB and AC.

Ans. Join OE and OF. Also join OA, OB and OC.

Since BD = 8 cm

BE = 8 cm

[Tangents from an external point to a circle are equal]

Since CD = 6 cm

CF = 6 cm

[Tangents from an external point to a circle are equal]

Let AE = AF =

Since OD = OE = OF = 4 cm

[Radii of a circle are equal]

Semi-perimeter of ABC = = cm

Area of ABC =

=

= cm2

Now, Area of ABC = Area of OBC + Area of OCA + Area of OAB

=

=

=

=

Squaring both sides,

AB = = 7 + 8 = 15 cm

And AC = = 7 + 6 = 13 cm


NCERT Solutions for Class 10 Maths Exercise 10.2

13. Prove that opposite sides of a quadrilateral circumscribing a circle subtend supplementary angles at the centre of the circle.

Ans. Given: ABCD is a quadrilateral circumscribing a circle whose centre is O.

To prove: (i) AOB + COD = (ii) BOC + AOD =

Construction: Join OP, OQ, OR and OS.

Proof: Since tangents from an external point to a circle are equal.

AP = AS,

BP = BQ ……….(i)

CQ = CR

DR = DS

In OBP and OBQ,

OP = OQ [Radii of the same circle]

OB = OB [Common]

BP = BQ [From eq. (i)]

OPB OBQ [By SSS congruence criterion]

[By C.P.C.T.]

Similarly,

Since, the sum of all the angles round a point is equal to

AOB + COD =

Similarly, we can prove that

BOC + AOD =

NCERT Solutions for Class 10 Maths Exercise 10.2

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17 thoughts on “NCERT Solutions for Class 10 Maths Exercise 10.2”

  1. While I was seeing it I found mistake in it in fig the name is change and in solutions it is change only in some of the questions otherwise it’s good

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