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Which of the following triangles are isosceles as well as obtuse-angled triangles?


Which Of The Following Triangles Are Isosceles As Well As o...


Options:
A .   Fig 1 and Fig 3 only
B .   Fig 2 and Fig 3 only
C .   Fig 1, Fig 2 and Fig 4 only
D .   Fig 1, Fig 2 and Fig 3 only
Answer: Option A
:
A

An obtuse angled triangle is the triangle in which one of the angles is greater than 90. 
An isosceles triangle is the triangle in which two sides are equal.
1. Fig 1:
ΔPQR  is isosceles [PQ=PR]
                          Q=R
[ angles opposite to equal sides of a triangle are equal]
P+Q+R  =180 
[angle sum property of a triangle]
P+25 +25 =180
P=180 50=130 
ΔPQR is an obtuse angled triangle as one of the angles measures 130°.
2. Fig 2:
ΔABC is isosceles [AB=AC]
Similarly as above, we can find the angles of this triangle.
A=35,B=C=72.5 
Since all angles are less than 90, ΔABC is an acute angled triangle.
3. Fig 3:
ΔXYZ is an isosceles as well as an obtuse angled triangle as angle Y measures 110°.
4. Fig 4:
ΔMNO is an isosceles as well as a right angled triangle.
Hence, only Fig 1 and Fig 3 are isosceles as well as obtuse angled triangles.



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