slope (rise over run)of blue/green is 2/5 slope of red is 3/8.
now for easy comparison the bluegreen is 16/40 while red is 15/40 thus the slopes are not equal and thuis the entire thing is not a triangle.
And yet that alone does not explain where the missing piece came from. all the pieces are the same size in both pictures, However the shape is slightly concave in the top picture, and slightly convex in the bottom picture, thus the "missing" piece is really spread over the length of the diagional in a very thin shape, and is hard to detect. but thats where it went