Question

LES
ABCD is a quadrilateral in which AD = BC and
DAB= Z CBA (see Fig. 7.17). Prove that
(1) A ABDEABAC
(ü) BD=AC
(i) ZABD=ZBAC.
​

Answer 1

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Congruence of triangles:

Two ∆’s are congruent if sides and angles of a triangle are equal to the corresponding sides and angles of the other ∆.

 

In Congruent Triangles corresponding parts are always equal and we write it in short CPCT i e, corresponding parts of Congruent Triangles.

 

It is necessary to write a correspondence of vertices correctly for writing the congruence of triangles in symbolic form.

 

Criteria for congruence of triangles:

There are 4 criteria for congruence of triangles.

SAS( side angle side):

Two Triangles are congruent if two sides and the included angle of a triangle are equal to the two sides and included angle of the the other triangle.

----------------------------------------------------------------------------------------------------

First

use, SAS rule to show congruence of triangles and then use CPCT to show ii

& iii parts.

Given:

In quadrilateral ABCD,

AD = BC &

∠DAB = ∠CBA

 

To Prove:

(i)             

ΔABD ≅ ΔBAC

(ii)           

BD=AC

(iii)          

∠ABD = ∠BAC

 

Proof:

i)

In ΔABD & ΔBAC,

AB = BA    (Common)

∠DAB = ∠CBA  (Given)

AD = BC (Given)

Hence,

ΔABD ≅

ΔBAC.        

( by SAS congruence rule).

(ii) Since, ΔABD ≅

ΔBAC

Then, BD = AC                                       (

by CPCT)

(iv)   Since, ΔABD ≅ ΔBAC

Then , ∠ABD = ∠BAC                         (by CPCT)

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Answer 2

Answer:

Step-by-step explanation:

Congruence of triangles:

Two ∆’s are congruent if sides and angles of a triangle are equal to the corresponding sides and angles of the other ∆.

 

In Congruent Triangles corresponding parts are always equal and we write it in short CPCT i e, corresponding parts of Congruent Triangles.

 

It is necessary to write a correspondence of vertices correctly for writing the congruence of triangles in symbolic form.

 

Criteria for congruence of triangles:

There are 4 criteria for congruence of triangles.

SAS( side angle side):

Two Triangles are congruent if two sides and the included angle of a triangle are equal to the two sides and included angle of the the other triangle.

----------------------------------------------------------------------------------------------------

First

use, SAS rule to show congruence of triangles and then use CPCT to show ii

& iii parts.

Given:

In quadrilateral ABCD,

AD = BC &

∠DAB = ∠CBA

 

To Prove:

(i)             

ΔABD ≅ ΔBAC

(ii)           

BD=AC

(iii)          

∠ABD = ∠BAC

 

Proof:

i)

In ΔABD & ΔBAC,

AB = BA    (Common)

∠DAB = ∠CBA  (Given)

AD = BC (Given)

Hence,

ΔABD ≅

ΔBAC.        

( by SAS congruence rule).

(ii) Since, ΔABD ≅

ΔBAC

Then, BD = AC                                       (

by CPCT)

(iv)   Since, ΔABD ≅ ΔBAC

Then , ∠ABD = ∠BAC                         (by CPCT)

=========================================================

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