#### Chapters

Chapter 2: Polynomials

Chapter 3: Pair of Linear Equations in Two Variables

Chapter 4: Quadratic Equations

Chapter 5: Arithmetic Progressions

Chapter 6: Triangles

Chapter 7: Coordinate Geometry

Chapter 8: Introduction to Trigonometry

Chapter 9: Some Applications of Trigonometry

Chapter 10: Circles

Chapter 11: Constructions

Chapter 12: Areas Related to Circles

Chapter 13: Surface Areas and Volumes

Chapter 14: Statistics

Chapter 15: Probability

## Chapter 6: Triangles

#### NCERT solutions for Class 10 Mathematics Textbook Chapter 6 Triangles Exercise 6.1 [Page 122]

Fill in the blanks using correct word given

All circles are __________.

congruent

similar

Fill in the blanks using correct word given

All squares are __________.

similar

congruent

Fill in the blanks using correct word given

All __________ triangles are similar.

isosceles

equilateral

Fill in the blanks using correct word given in the brackets:−

Two polygons of the same number of sides are similar, if (a) their corresponding angles are __________ and (b) their corresponding sides are __________. (equal, proportional)

Give two different examples of pair of similar figures

Give two different examples of pair of Non-similar figures

State whether the following quadrilaterals are similar or not:

#### NCERT solutions for Class 10 Mathematics Textbook Chapter 6 Triangles Exercise 6.2 [Pages 128 - 129]

See the given Figure. DE || BC. Find EC

See the given Figure. DE || BC. Find AD

E and F are points on the sides PQ and PR respectively of a ΔPQR. For the following case, state whether EF || QR. PE = 3.9 cm, EQ = 3 cm, PF = 3.6 cm and FR = 2.4 cm

E and F are points on the sides PQ and PR respectively of a ΔPQR. For the following case, state whether EF || QR

PE = 4 cm, QE = 4.5 cm, PF = 8 cm and RF = 9 cm

E and F are points on the sides PQ and PR respectively of a ΔPQR. For the following case, state whether EF || QR. PQ = 1.28 cm, PR = 2.56 cm, PE = 0.18 cm and PF = 0.36 cm

In the following figure, if LM || CB and LN || CD, prove that `(AM)/(AB)=(AN)/(AD)`

In the following figure, DE || AC and DF || AE. Prove that `(BF)/(FE)=(BE)/(EC)`

In the following figure, DE || OQ and DF || OR, show that EF || QR

In the following figure, A, B and C are points on OP, OQ and OR respectively such that AB || PQ and AC || PR. Show that BC || QR.

Using Basic proportionality theorem, prove that a line drawn through the mid-points of one side of a triangle parallel to another side bisects the third side. (Recall that you have proved it in Class IX).

Using Converse of basic proportionality theorem, 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).

ABCD is a trapezium in which AB || DC and its diagonals intersect each other at the point O. Show that `(AO)/(BO) = (CO)/(DO)`

The diagonals of a quadrilateral ABCD intersect each other at the point O such that** **`(AO)/(BO) = (CO)/(DO)` Show that ABCD is a trapezium

#### NCERT solutions for Class 10 Mathematics Textbook Chapter 6 Triangles Exercise 6.3 [Pages 138 - 141]

State which pair of triangles in the following figure are similar? Write the similarity criterion used by you for answering the question and also write the pairs of similar triangles in the symbolic form:

State which pair of triangles in the given figure are similar? Write the similarity criterion used by you for answering the question and also write the pairs of similar triangles in the symbolic form:

State which pair of triangles in the following figure are similar? Write the similarity criterion used by you for answering the question and also write the pairs of similar triangles in the symbolic form:

State which pair of triangles in the following figure are similar? Write the similarity criterion used by you for answering the question and also write the pairs of similar triangles in the symbolic form:

In the following figure, ΔODC ∼ ΔOBA, ∠BOC = 125° and ∠CDO = 70°. Find ∠DOC, ∠DCO and ∠OAB

Diagonals AC and BD of a trapezium ABCD with AB || DC intersect each other at the point O. Using a similarity criterion for two triangles, show that `(AO)/(OC) = (OB)/(OD)`

In the following figure, `(QR)/(QS) = (QT)/(PR) ` and ∠1 = ∠2. Show that ΔPQS ~ ΔTQR.

S and T are point on sides PR and QR of ΔPQR such that ∠P = ∠RTS. Show that ΔRPQ ∼ ΔRTS.

In the following figure, if ΔABE ≅ ΔACD, show that ΔADE ∼ ΔABC.

In the following figure, altitudes AD and CE of ΔABC intersect each other at the point P. Show that:

ΔAEP ∼ ΔCDP

In the following figure, altitudes AD and CE of ΔABC intersect each other at the point P. Show that:

ΔABD ∼ ΔCBE

In the following figure, altitudes AD and CE of ΔABC intersect each other at the point P. Show that:

ΔAEP ∼ ΔADB

In the following figure, altitudes AD and CE of ΔABC intersect each other at the point P. Show that:

ΔPDC ∼ ΔBEC

E is a point on the side AD produced of a parallelogram ABCD and BE intersects CD at F. Show that ΔABE ∼ ΔCFB

In the following figure, ABC and AMP are two right triangles, right angled at B and M respectively, prove that:

ΔABC ~ ΔAMP

` (CA)/(PA) = (BC)/(MP)`

CD and GH are respectively the bisectors of ∠ACB and ∠EGF such that D and H lie on sides AB and FE of ΔABC and ΔEFG respectively. If ΔABC ~ ΔFEG, Show that

(i) `(CD)/(GH) = (AC)/(FG)`

(ii) ΔDCB ~ ΔHGE

(iii) ΔDCA ~ ΔHGF

In the following figure, E is a point on side CB produced of an isosceles triangle ABC with AB = AC. If AD ⊥ BC and EF ⊥ AC, prove that ΔABD ∼ ΔECF

Sides AB and BC and median AD of a triangle ABC are respectively proportional to sides PQ and QR and median PM of ΔPQR (see the given figure). Show that ΔABC ∼ ΔPQR.

D is a point on the side BC of ∆ABC such that ∠ADC = ∠BAC. Prove that ` \frac{CA}{CD}=\frac{CB}{CA} or, CA^2 = CB × CD.`

Sides AB and AC and median AD of a triangle ABC are respectively proportional to sides PQ and PR and median PM of another triangle PQR. Show that ΔABC ~ ΔPQR

A vertical pole of a length 6 m casts a shadow 4m long on the ground and at the same time a tower casts a shadow 28 m long. Find the height of the tower.

AD and PM are medians of triangles ABC and PQR, respectively where Δ ABC ~ Δ PQR, prove that `("AB")/("PQ") = ("AD")/("PM")`

#### NCERT solutions for Class 10 Mathematics Textbook Chapter 6 Triangles Exercise 6.4 [Pages 143 - 144]

Let Δ ABC ~ Δ DEF and their areas be, respectively, 64 cm^{2} and 121 cm^{2}. If EF = 15.4 cm, find BC

Diagonals of a trapezium ABCD with AB || DC intersect each other at the point O. If AB = 2CD, find the ratio of the areas of triangles AOB and COD.

In Figure, ABC and DBC are two triangles on the same base BC. If AD intersects BC at O, show that `(ar(ABC))/(ar(DBC)) = (AO)/(DO)`

If the areas of two similar triangles are equal, prove that they are congruent

D, E and F are respectively the mid-points of sides AB, BC and CA of ΔABC. Find the ratio of the area of ΔDEF and ΔABC.

Prove that the ratio of the areas of two similar triangles is equal to the square of the ratio of their corresponding medians.

Prove that the area of an equilateral triangle described on one side of a square is equal to half the area of the equilateral triangle described on one of its diagonals

ABC and BDE are two equilateral triangles such that D is the mid-point of BC. Ratio of the area of triangles ABC and BDE is

2 : 1

1 : 2

4 : 1

1 : 4

Sides of two similar triangles are in the ratio 4 : 9. Areas of these triangles are in the ratio

2 : 3

4 : 9

81 : 16

16 : 81

#### NCERT solutions for Class 10 Mathematics Textbook Chapter 6 Triangles Exercise 6.5 [Pages 150 - 151]

Sides of triangle are given below. Determine it is a right triangle or not? In case of a right triangle, write the length of its hypotenuse. 7 cm, 24 cm, 25 cm

Sides of triangles are given below. Determine it is a right triangles? In case of a right triangle, write the length of its hypotenuse. 3 cm, 8 cm, 6 cm

Sides of triangle are given below. Determine it is a right triangle or not? In case of a right triangle, write the length of its hypotenuse. 50 cm, 80 cm, 100 cm

Sides of triangle are given below. Determine it is a right triangle or not? In case of a right triangle, write the length of its hypotenuse. 13 cm, 12 cm, 5 cm

PQR is a triangle right angled at P and M is a point on QR such that PM ⊥ QR. Show that PM^{2} = QM . MR

In Figure, ABD is a triangle right angled at A and AC ⊥ BD. Show that AB^{2} = BC × BD

In Figure ABD is a triangle right angled at A and AC ⊥ BD. Show that AC^{2} = BC × DC

In Figure, ABD is a triangle right angled at A and AC ⊥ BD. Show that AD^{2} = BD × CD

ABC is an isosceles triangle right angled at C. Prove that AB^{2} = 2AC^{2}

ABC is an isosceles triangle with AC = BC. If AB^{2} = 2AC^{2}, prove that ABC is a right triangle.

ABC is an equilateral triangle of side 2a. Find each of its altitudes.

Prove that the sum of the squares of the sides of a rhombus is equal to the sum of the squares of its diagonals

In the following figure, O is a point in the interior of a triangle ABC, OD ⊥ BC, OE ⊥ AC and OF ⊥ AB. Show that

(i) OA^{2} + OB^{2} + OC^{2} − OD^{2} − OE^{2} − OF^{2} = AF^{2} + BD^{2} + CE^{2}

(ii) AF^{2} + BD^{2} + CE^{2 }= AE^{2} + CD^{2} + BF^{2}

A ladder 10 m long reaches a window 8 m above the ground. Find the distance of the foot of the ladder from base of the wall.

A guy wire attached to a vertical pole of height 18 m is 24 m long and has a stake attached to the other end. How far from the base of the pole should the stake be driven so that the wire will be taut?

An aeroplane leaves an airport and flies due north at a speed of 1,000 km per hour. At the same time, another aeroplane leaves the same airport and flies due west at a speed of 1,200 km per hour. How far apart will be the two planes after `1 1/2` hours?

Two poles of heights 6 m and 11 m stand on a plane ground. If the distance between the feet of the poles is 12 m, find the distance between their tops.

D and E are points on the sides CA and CB respectively of a triangle ABC right angled at C. Prove that AE^{2 }+ BD^{2} = AB^{2} + DE^{2}

The perpendicular from A on side BC of a Δ ABC intersects BC at D such that DB = 3CD . Prove that 2AB^{2} = 2AC^{2} + BC^{2}.

In an equilateral triangle ABC, D is a point on side BC such that BD = `1/3BC` . Prove that 9 AD^{2} = 7 AB^{2}

In an equilateral triangle, prove that three times the square of one side is equal to four times the square of one of its altitudes.

Tick the correct answer and justify: In ΔABC, AB = `6sqrt3` cm, AC = 12 cm and BC = 6 cm.

The angle B is:

120°

60°

90°

45°

#### NCERT solutions for Class 10 Mathematics Textbook Chapter 6 Triangles Exercise 6.6 [Pages 152 - 153]

In the given figure, PS is the bisector of ∠QPR of ΔPQR. Prove that `(QS)/(SR) = (PQ)/(PR)`

In the given figure, D is a point on hypotenuse AC of ΔABC, DM ⊥ BC and DN ⊥ AB, Prove that:

(i) DM^{2} = DN.MC

(ii) DN^{2} = DM.AN

In the given figure, ABC is a triangle in which ∠ABC> 90° and AD ⊥ CB produced. Prove that AC^{2} = AB^{2} + BC^{2} + 2BC.BD.

In the given figure, ABC is a triangle in which ∠ABC < 90° and AD ⊥ BC. Prove that AC^{2} = AB^{2} + BC^{2} − 2BC.BD.

In the given figure, AD is a median of a triangle ABC and AM ⊥ BC. Prove that:

1)`AC^2 = AD^2 + BC . DM + ((BC)/2)^2`

2)` AB^2 = AD^2 – BC . DM + ((BC)/2)^2`

3)` AC^2 + AB^2 = 2 AD^2 + 1/2(BC)^2`

Prove that the sum of the squares of the diagonals of parallelogram is equal to the sum of the squares of its sides.

In the given figure, two chords AB and CD intersect each other at the point P. prove that:

(i) ΔAPC ∼ ΔDPB

(ii) AP.BP = CP.DP

In the given figure, two chords AB and CD of a circle intersect each other at the point P (when produced) outside the circle. Prove that

(i) ΔPAC ∼ ΔPDB

(ii) PA.PB = PC.PD

In the given figure, D is a point on side BC of ΔABC such that ∠ADC=∠BAC . Prove that AD is the bisector of ∠BAC.

Nazima is fly fishing in a stream. The tip of her fishing rod is 1.8 m above the surface of the water and the fly at the end of the string rests on the water 3.6 m away and 2.4 m from a point directly under the tip of the rod. Assuming that her string (from the tip of her rod to the fly) is taut, ho much string does she have out (see Figure)? If she pulls in the string at the rate of 5 cm per second, what will be the horizontal distance of the fly from her after 12 seconds?

## Chapter 6: Triangles

## NCERT solutions for Class 10 Mathematics Textbook chapter 6 - Triangles

NCERT solutions for Class 10 Mathematics Textbook chapter 6 (Triangles) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CBSE Class 10 Mathematics Textbook solutions in a manner that help students grasp basic concepts better and faster.

Further, we at Shaalaa.com provide such solutions so that students can prepare for written exams. NCERT textbook solutions can be a core help for self-study and acts as a perfect self-help guidance for students.

Concepts covered in Class 10 Mathematics Textbook chapter 6 Triangles are Similar Figures, Similarity of Triangles, Basic Proportionality Theorem Or Thales Theorem, Criteria for Similarity of Triangles, Areas of Similar Triangles, Pythagoras Theorem, Similarity Triangle Theorem, Application of Pythagoras Theorem in Acute Angle and Obtuse Angle, Triangles Examples and Solutions, Angle Bisector, Similarity Examples and Solutions, Ratio of Sides of Triangle, Similar Figures, Similarity of Triangles, Basic Proportionality Theorem Or Thales Theorem, Criteria for Similarity of Triangles, Areas of Similar Triangles, Pythagoras Theorem, Similarity Triangle Theorem, Application of Pythagoras Theorem in Acute Angle and Obtuse Angle, Triangles Examples and Solutions, Angle Bisector, Similarity Examples and Solutions, Ratio of Sides of Triangle.

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