givio

I'm math challenged... I want to make an octagon using triangles (that point toward the center of the octagon), then mirror image the triangle (so it becomes a diamond), and have a resulting star. How do I figure out what the length of the sides of the triangles should be? The short side of the triangle will make the octagon, and the other two sides of the triangle will be equal and longer. If I make the short side of the triangle, for example, 6", then what will be the length of the other two sides?

Siodach

Hi there
its not so much about the length, as it is about the angles in the centre. An (imaginary) circle in the middle uses 360 degrees. To get 8 sections you divide 360 by 8. This gives you a centre angle of 45 degrees for each section of your octagonal shape.

You probably have a 45 degree triangle ruler already lol.

With this angle you can then go ahead and make your sides whatever you need them to be, provided you keep both sides the same. The third length across the outside will sort itself out.

Try it out with a bit of paper first :-))

If you want a 5-pointed star you'd divide 360 by 5.
6-points, divide 360 by 6
Etc........

Ariannaquilts

Wow Siodach very impressive!

ManiacQuilter2

You can get a diamond 45 degree from half square triangles??? If you don't have EQ, you might want to draft out the proportion of a quilt. I took drafting in college and so glad I did.

givio

Siodach, Thanks! That's just the info I wanted. :-) In the meantime, I also found these nifty calculators: https://rechneronline.de/pi/octagon.php
http://www.htmliseasy.com/octagon_layout/

Jan in VA

She never mentioned HSTs. I'm sure she was thinking either isosceles or equilateral triangles; this whole topic is an interesting one. Good thing we have the brilliant Scot among us!

Love your name, Siodach. Please tell us how it is pronounced.

Jan in VA

Siodach

Hi there
jan is correct in that HSTs wouldn't do in this instance, because the two sides coming away from the 45 degree point are NOT equal in length in a HST and they need to be equal in Givio's design.

I don't know about brilliant, but I was born in England and came to Scotland in 1972, so regard myself as a naturalised scot by now lol.

SIODACH is a Gaelic word, pronounced (as close as I can get lol) 'shuh-da-cchh', where the cchh is soft at the back of your throat as in 'loch' .

It means 'silky', particularly as a description of hair, and dates back to the time when I bred Persian cats. Siodach was/is my cattery name (and it will remain mine until 50 years after my death, he he). The word has the great advantage that if I want to sign up for something, that name has never been already taken lol.

Jan in VA

I thought for sure the name was Gaelic, and the meaning of "silky" puts me in mind of the stories of the silkies in Diana Gabaldon's Outlander series. LOVE these books!! And I'm now totally captivated with all things Scottish, especially after finding on AncestryDNA that my own heritage is majorly Scot/English, virtually no Irish, and 8% "Scandinavian" -- thinking that MUST be the Viking influence! Less than 10% rest of the world in my genes, so strange.

Jan in VA