Question

find the number of sides of a rectangular polyon having 20 sides

Answer 1

Answer:

20×4 = 80

Step-by-step explanation:

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Answer 2

Answer:

A regular polygon has 20 sides. How many triangles can be drawn by using the vertices, but not using the sides?

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The number of all triangles using the vertices and sides is a combination of 20 taking 3 at a time.

20c3=20!/(3! x 17!)=1140……………………………………………….. A

Let us number the sides as 1,2,3…20

Now consider triangles that has one side of the polygon as it’s side.

If we take one side , we can form 18 triangles, so it comes to 360……B .

If we take two sides, we can form 20 triangles.( 1–2,2–3,…….19–20,20–1)…..C

We can not form triangles taking 3 sides of the polygon.

Hence number of trianles that can be formed using only vertices of the 20 sided polygon is

A-B-C= 1140–360–20= 760.