Here are a few online services which offer graphing functionality:

• Desmos (2D only)
• Math3d—a bit rough around the edges, but works well once you figure out the quirks. From what I can tell it doesn't understand juxtaposition multiplication with variables, i.e. you need to write $$\sin(n\cdot\theta)$$ instead of $$\sin(n\theta).$$
1. Graph a torus with major radius $$K$$ and minor radius $$k .$$
2. Graph a Möbius strip.