In a closed polygon, there are 35 diagonals. How many sides does the polygon have?


Answer: 10

ant101  Jun 3, 2018

Hello, again Ant101!


The formula to find the number of diagonals in a closed polygon is: \(\frac{n(n-3)}{2}\) , where n is the number of sides.


Since there are 35 diagonals in the polygon, we can let the above formula equal 35.


So, we have: \(\frac{n(n-3)}{2}=35\)


Taking 2 to the other side, we have: \(n(n-3)=70\)


We need to find a value of n that suits this scenario, therefore \(\boxed{10}\) sides is our answer!


Check: 10*(10-3)=70, 10*7=70, yep!


tertre  Jun 3, 2018

The formula to find the number of diagonals = n(n-3)/2, where n = no. of sides of the polygon.

Here n(n-3)/2 = 35, or

n(n-3) = 70

n^2 - 3n - 70 = 0, or

(n-10)(n+7) = 0, lor

n = 10 or -7.

Guest Jun 3, 2018

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