Arcs
Another natural curve is an arc: slices from a pie (or ellipse). Again the API for drawing these in SVG directly is a bit unfriendly. But the solution is a bit more obvious this time. Three parameters: start angle, end angle and radius. Pretty simple.
<path
d="M 390.71067811865476 390.71067811865476 A 100 100 0 1 0 264.4429766980398 403.14696123025453"
stroke="black"
fill="transparent"
strokeWidth="3"
/>
The angles need to be between 0 and 2π, otherwise things get glitchy (but maybe fun):