Congruence of Triangles By SSS Criteria


 
 
Concept Explanation
 

Congruence of Triangles by SSS Criteria

Theorem: Two triangles are congruence if the three sides of one triangle are equal to the corresponding three sides of the other triangle.

Given: Two large Delta sABC; and; DEF such that AB = DE, BC = EF and AC = DF.

To Prove: large Delta ABCcong Delta DEF

Construction: Draw a line segment EG on the other side of EF such that AB = EG and large angle ABC = angle FEG. Join GF and GD.

Proof:  In large Delta ABC  and large Delta GEF, we have

              BC = EF                                [Given]

              AB = GE                         [By construction]

and, large angle ABC=angle FEG    [By construction]

So, by SAS criterion of congruence, we have

          large Delta ABCcong Delta GEF

large Rightarrow ;;angle A=angle G;and;AC=GF                           [C.P.C.T.]

Now, AB = DE and AB = GE

large Rightarrow ;;DE=GE                                                              ....(i)

Similarly, AC = DF and AC = GF

large Rightarrow ;;DF=GF

In large Delta EGD, we have                                            [From (i)]

          DE = GE                                                             ....(iii)

large Rightarrow ;;;angle EDG=angle EGD

In large Delta FGD, we have

         DF = GF                                                   [From (ii)]

large Rightarrow ;;;angle FDG=angle FGD                      ....(iv)

From (iii) and (iv), we have

      large angle EDG+angle FDG=angle EGD+angle FGD

large Rightarrow ;;;;;angle D=angle G                                  [Proved above]

But,        large Rightarrow ;;;;;angle G=angle A                       ....(v)

large therefore ;;;;angle A=angle D

Thus, in large Delta sABC and DEF, we have

       AB = DE                                           [Given]

      large angle A=angle D                                [From (v)]

and,    AC = DF                                       [Given]

So, by SAS criterion of congruence , we have

large Delta ABCcong Delta DEF 

Illustration: ABCD is a parallelogram , if the two diagonals are equal, find the measure of large angle ABC

Solution: Since ABCD is a parallelogram. Therefore,

                  AB = CD and AD = BC           [ large because Opposite sides of a parallelogram are equal]

Thus, in large Delta sABD and ACB, we have

          AD = BC                  [As proved above]

         BD = AC                          [Given]

and,   AB = AB                       [common]

So, by SSS criterion of congruence, we have

      large Delta ABD cong Delta ACB

large Rightarrow ;;angle BAD = angle ABC

Now,  large ADparallel BC and transversal AB intersects them at A and B respectively.

large therefore ;;;angle BAD+angle ABC=180^{circ}          [Sum of the interior angles on the same side of a

                                                                                 transversal is large 180^{circ}]

large Rightarrow ;;;angle ABC+angle ABC=180^{circ}

large Rightarrow ;;;2angle ABC=180^{circ}

Rightarrow angle ABC=frac{180^{0}}{2}

large Rightarrow ;;;angle ABC=90^{circ}

Hence, the measure of large angle ABC;is;90^{circ}.

Sample Questions
(More Questions for each concept available in Login)
Question : 1

Two isosceles triangles  ABC and DBC having the common base BC such that AB = AC and DB = DC. Then bigtriangleup ABDcong bigtriangleup ACD by which criterion?

Right Option : B
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Explanation
Question : 2

In the given figure, AD is the median then ∠BAD is  

Right Option : D
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Explanation
Question : 3

In the figure shown above, if AB = DE, AC = DF and BC = EF, then which two triangles are congruent?

Right Option : C
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Explanation
 
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