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Q.

State true or false:


Triangle is a polygon whose sum of exterior angles is double the sum of interior angles.


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a

True

b

False 

answer is A.

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Detailed Solution

Given a statement, triangle is a polygon whose sum of exterior angles is double the sum of interior angles.
We need to find whether the given statement is true or false.
The angle sum property of a polygon says that the sum of all the interior angles of a triangle is always 180 .
Now, we know that with every interior angle, there exists an exterior angle which is formed by a side of a triangle and an extension of the adjacent side.
So, let us consider a triangle with its interior and exterior angles as follows,
Question ImageNow, applying the angle sum property in the above triangle, we get,
x+y+z= 180 ° .........(i)
Now, we know that a pair of an exterior and interior angle at a location is always supplementary.
Using this fact, we can express the exterior angles of the triangle in terms of its interior angles as follows,
p+x= 180 p= 180 x........(ii) q+y= 180 q= 180 y........(iii) r+z= 180 r= 180 z.........(iv)
Adding the equations (ii), (iii) and (iv), we get,
p+q+r= 180 x+ 180 y+ 180 z p+q+r= 540 xyz p+q+r= 540 (x+y+z).........(v)
Substituting the value of x+y+z from equation (i) in (iv), we get,
p+q+r= 540 180 p+q+r= 360
So, we can observe that the sum of the exterior angles of the triangle is 360 , which is just double of the sum of its interior angles, i.e., 180 .
Hence, the statement is true.
Hence, the correct option is (1).
 

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