Here is an easy way to make triangles on the corners of square patches without cutting triangles and working with stretchy bias edges.

Prep: Cut (1) 3" square and (2) 1 3/4" squares

With right sides together, align a small square in one corner of the 3" square as shown. Draw a seam line diagonally from corner to corner of the small square. Sew on the line. Trim seam allowances to 1/4", flip open and press toward the corner.

Likewise, sew a small square to the adjacent corner of the 3" square. Trim and press.

There are lots of ways to use this technique. Cut more 1 3/4" squares and continue sewing the squares around the base fabric for a "square in a square" block. Make flying geese blocks using a 1 3/4" x 3" base fabric and the same size squares. If you make the 1 3/4" squares smaller and sew to the base fabric on all four corners you now have a snowball block. Think of the possibilities!