21. Let P be a regular twelve-sided polygon. The number of right-angled
triangles formed by the vertices of P is
(A) 60
B) 120
(C) 160
(D) 220.
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Answer:answer is 60(A)
Explanation - we can get 90 degree angle only when a line joining two opposite vertices of the polygon form the 2 vertex of triangle..(property of circle)
No. Of right angled traingles=10*6=60
(as there can be 12/2=6 lines joining 12 opposite vertices, and in each triangle the third vertex can be be anyone among the 10 vertex left)
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