Math Is Fun Forum
You are not logged in.
- Topics: Active | Unanswered
#1 2008-04-15 15:23:06
- stellina91
- Member
- Registered: 2008-04-15
- Posts: 12
Polygon
Find the value of a in the diagram, giving all reasons
My attempt:
180(5-2) = 540 (What would be the reason here? E.g. Interior angle sum of an irregular pentagon)
2a + a + 104 + 125 + 107 = 540
3a + 336 = 540
3a = 204
a = 68
Thanks.
Offline
#2 2008-04-15 16:20:39
- LuisRodg
- Real Member
- Registered: 2007-10-23
- Posts: 322
Re: Polygon
Your right. What do you need help with? Just checking if you were right?
Offline
#3 2008-04-15 16:23:12
- Dragonshade
- Member
- Registered: 2008-01-16
- Posts: 147
Re: Polygon
You will see in this way. When you divided it into 3 triangle, the sum of interior is actually the sum of the interior of the 3 triangles , so 3*180=540 degree
Offline
#4 2008-04-15 16:25:43
- LuisRodg
- Real Member
- Registered: 2007-10-23
- Posts: 322
Re: Polygon
Theres actually a formula to figuring out the sum of the angles of a polygon:
180(n-2) where n is the sides of the polygon.
Which I see he/she used by doing 180(5-2) = 540.
Offline
#5 2008-04-15 16:27:46
- Dragonshade
- Member
- Registered: 2008-01-16
- Posts: 147
Re: Polygon
Theres actually a formula to figuring out the sum of the angles of a polygon:
180(n-2) where n is the sides of the polygon.
Which I see he/she used by doing 180(5-2) = 540.
yea, but he wanted to know why
Offline
#6 2017-05-19 15:59:55
- Monox D. I-Fly
- Member
- From: Indonesia
- Registered: 2015-12-02
- Posts: 2,000
Re: Polygon
LuisRodg wrote:Theres actually a formula to figuring out the sum of the angles of a polygon:
180(n-2) where n is the sides of the polygon.
Which I see he/she used by doing 180(5-2) = 540.
yea, but he wanted to know why
Well, I have tried to prove that, using sectors of a circle. Make a circle, then divide it to five equal sectors. After that, make a regular pentagon inside the circle. Each sector will have 72° as their radius angle. From this, you can know that each angle of the pentagon is 108°. Multiplying it by 5 will give 540°. You can do for other polygons to get similar proof.
Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away.
May his adventurous soul rest in peace at heaven.
Offline