How many diagonals are there in a N-gon?

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[saismile]

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[jarhcoming]

Selection of two points = nc2 and subtracting n as adjacent sides do not form diagonal So
nc2 - n
=(n!/((2!)(n-2)!))-n
=(n(n-1)/2) - n
= n(n-3)/2

[moonsmagic]

The fact that this was posted after my math exam and I had a question which required to use this formula is just...✨coincidence✨

[messifanpage]

There will be 170 diagonals ❤️ [20(20-3)]/2
= (20×17)/2 = 17×10= 170

[НубикПубиквКыргызстане]

Please explain which diagonals are you talking about?

[BeeKreatib]

N (N-3) /2
= 20 (20-3) /2
= 20 (17) /2
= 340/2
= 170 :)

[GhossounDaraghmeh]

20x17=340 340/2=170 😊

[SmashiWithTheMen]

Because 20(20-3)÷2 is worked out by 20-3=17×20=340÷2=170 if I am wrong I'm just a 9 year old kid

[Zainab-twcb]

I actually did it in my head and got 170. Thanks alot🥰

[umeshchandrapandey]

n(n-3)/2
So for a 20gon
20(20-3)/2
=10(17)
=170
That means a 20gon has 170 diagonals.

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