India Math Olympiad Math Olympiad PRMO

Direction & Angles | PRMO-2019 | Problem 4

Try this beautiful problem from PRMO, 2019, problem-4, based on Geometry: Direction & Angles. You may use sequential hints to solve the problem.

Try this beautiful Geometry problem from PRMO, 2019 based on Direction & Angles.

Direction & Angles | PRMO | Problem-4

An ant leaves the anthill for its morning exercise. It walks 4 feet east and then makes a 160° turn to the right and walks 4 more feet. It then makes another 160° turn to the right and walks 4 more feet. If the ant continues this pattern until it reaches the anthill again, what is the distance in feet it would have walked?

  • $20$
  • $36$
  • $13$

Key Concepts


Co-ordinate geometry


Check the Answer


PRMO-2018, Problem 13

Pre College Mathematics

Try with Hints

Direction & Angles - figure

According to the problem we draw the figure and try to solve using co-ordinate method…

Can you now finish the problem ……….

Let \(A_0(0,0)\)

Therefore \(A_1(4 cos 0,4sin 0)\)

\(A_2(4cos 0+4 cos 160, 4 sin 0+4 sin 160)\)

\(\Rightarrow A_n =(0,0)\)

and \(4(cos 0+cos 160 +…+sin 160(n-1)=0\)

\(\Rightarrow n =9\)

Can you finish the problem……..

Therefore distance covered =\(4 \times 9\)=\(36\)

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