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.
ASA(angle side angle):
Two Triangles are congruent if two angles
and the included side of One triangle are equal to two angles & the
included side of the other triangle.
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Given,
l is the bisector of an angle ∠A i.e, ∠BAP = ∠BAQ
BP and BQ are perpendiculars.
To prove:
i) ΔAPB ≅ ΔAQB
ii)
BP = BQ or B is equidistant from the arms of ∠A.
Proof:
(i)
In ΔAPB and ΔAQB,
∠P = ∠Q. (90°)
∠BAP = ∠BAQ (l is bisector)
AB = AB (Common)
Hence,
ΔAPB ≅ ΔAQB (by
AAS congruence rule).
(ii) since ΔAPB ≅
ΔAQB,
Then,
BP
BQ. (by CPCT.)
Hence,
B is equidistant from the arms of ∠A.
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