How to Cut Isosceles Triangle
 

I have seen a photo of a pretty Christmas cushion made from Isosceles triangles. (2 long sides, 1 short)

Is there a trick to cutting these or will I need to buy a template?

For a pillow I'd probably make a template, for a quilt I use the Tri Recs Ruler to make life easy.
here is a demo o the ruler, https://www.youtube.com/watch?v=HQCdh-ZkRAM
and a demo of fitting them together so they come out right
https://www.youtube.com/watch?v=aTPE1EFZHpc

and if this isn't an isosceles, sorry :)

Yes, that’s the triangle I’m after!
Thanks for the YouTube links - they’re really helpful.

Just worked out how to copy link to cushion photo from Pinterest -

https://pin.it/qb3eg2l2t5i6ox

I just remembered I've also foundation paper pieced
https://www.generations-quilt-patter...ilt-block.html
and also if you like the technique you could english paper piece them :) An easy to get along with technique!

looking at your pattern the block technique shown on the first two links wouldn't work because you are not looking for a block but a series of triangles.

Thanks for your addition comments.

I have done a little EPP but don’t really fancy that for this project.

I think I might just try getting a piece of paper the size of the cushion top and draw out the design.
Even if this just gets me the size of the angles it would be a starting point.

One of my bookmarked sites is this one, maybe one of their graphs will help you out
https://www.incompetech.com/graphpaper/

Here's a sublinks just on one triangle option:
https://www.incompetech.com/graphpaper/vartriangle/

Thanks Iceblossom - your links are very helpful.
What a useful tool!

When I’ve looked at the cushion again I realised I’ve been over-thinking this.

If I make the cushion 16” the triangles block could be 15”. (Plus an additional narrow border)

There are 5 triangles across the block. Finished width would be 3” each.

There are 4 rows so the triangles will be 3.75” high.

I should be able to draw the triangles. :D

Tri Rec's ruler strongly suggested.

Just saying --be careful what angle your ruler gives you. I made several of the kaleidoscope quilts and made the mistake of getting the TriRec ruler. The angle is not correct for those! There is a pattern included with the TriRec that is good for those rulers though. The angle of the triangle/ruler will determine how many "blades" it takes to make the full circle.

Can/Will you post a sketch of what you have in mind.

I learned, the hard way, that the triangle in a square unit has different angles that 30-60-90 and 60-60-60!

Attached is a drawing of the triangle in a square unit with the angles to the nearest thousandth of a degree.

360 divided by 7 equals 51.429 degrees, so the Tri-Recs ruler is not appropriate for a circle evenly divided by 7. The "center angle" of the larger ruler is approximately 53.130 degrees, which multiplied by 7 equals approximately 371.910 degrees.

I have zero experience with sewing isosceles triangles. So my approach would be to draft a couple of the triangles on graph paper, add seam allowances, cut out, sew together (with dull needle from my quilt lab/paper sewing needle stash) to check for any problems, then proceed from there.
Fell in love with the Alaska quilt by Edyta Sitar and bought her pattern and Eleanor Burns' Kaleidoscope II pattern to do a practice piece. However, these make a circle, totally different animal than the isosceles used here for your pillow.
Oh! The math!! Everything ends up with the math. But I guess it's the mental challenge of quilting that always keeps us coming back for more.:p

Quilt in a Day has the ruler made for this. https://www.quiltinaday.com/shoponline/ruler/702
I used it to make the Pieces of Life quilt several years ago and I never lost a point. There is a video of how to use it at the link.

I agree that there are four rows.

It looks to me like there are 6 trees in the top row, 5 in the second row, 6 in the third row, and 5 trees in the bottom row. (If I were making it, I would have 6 trees in the bottom row, and a 5 tree row on the top.)

I think the maker used cording around the edge of the pillow.

I think the ratio that would work would be a width to height ratio of 2:3.

Example, If the base of the triangle is two inches, the height would be 3 inches. (2 x 6 = 12 for the width and 4 x 3 = 12 for the height)

Base - 2.5, Height - 3.75 (2.5 x 6 = 15 for the width, and 4 x 3.75 = 15 for the height)

Base - 3, Height - 4.5 ( 18 for the width, 18 for the height)

You can change the ratio to whatever looks attractive to you.

The triangle-in-a-square tool/ruler (Tri-Recs), the base of the "fat" triangle is equal to the height.

I have attached another drawing for comparison of the triangles, using 3.75 inches for the height.

Remember to add seam allowances! Dimensions do not include seam allowances.