Dot to Dot on x-y plane

Geometry Level 2

Starting from the origin on the x y x y plane I make a straight line to any point with integer coordinates. I then make a straight line from that integer coordinate to another integer coordinate. I continue this for as many lines as I wish until I return the origin again.

Let a a be the number of integer coordinates touching the lines that I have drawn.

Let b b be the number of integer coordinates enclosed by the shape that I have drawn (not touching the lines).

If a = 44 a = 44 and b = 61 b = 61 , what is the area of the region enclosed by the lines I have drawn?

Note:

  • The lines cannot intersect each other.

  • The lines cannot return to a coordinate with a line already passing through it, ending or starting on it.

Example:

( 0 , 0 ) (0,0) \rightarrow ( 0 , 2 ) (0,2) \rightarrow ( 2 , 2 ) (2,2) \rightarrow ( 2 , 0 ) (2,0) \rightarrow ( 0 , 0 ) (0,0)

a = 8 , b = 1 a = 8, b = 1 Area enclosed by region = 4 =4


The answer is 82.

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1 solution

By Pick's theorem , we get the area of the polygon = 1 2 \dfrac{1}{2} ( number of boundary points ) + + number of interior points 1 -1 = 44 2 + 61 1 = 82 \dfrac{44}{2}+61-1=\boxed {82}

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