__maths__>__Construction / Practical Geometry (basics)__>__Standard angles Using Campus__### Constructing `120^@` using a compass

In this page, a short and to-the-point overview of constructing `120^@` angle using a compass is provided.

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Which of the following help to construct `120^@` angle using a compass?

- construct `60^@` on top of another `60^@` angle. Both together form `120^@`
- construct `60^@` on top of another `60^@` angle. Both together form `120^@`
- `120^@` angle cannot be constructed using a compass

The answer is "construct `60^@` on top of another `60^@` angle. Both together form `120^@`"

Constructing `60^@` angle twice-over to construct `120^@` • With an arbitrary distance-measure on compass, mark point `P` from point `A` on line `bar(AB)`.

• With the same distance measure on compass, construct two arcs from points `A` and `P`. The arcs cut at point `Q`. `bar(AQ)` makes `60^@` with the `bar(AP)`.

• With the same distance measure on compass, construct two arcs from points `A` and `Q`. The arcs cut at point `R`. `bar(AR)` makes `120^@` with the `bar(AP)`. The angle `120^@` is constructed as `/_PAR`.

**Constructing `120^@` angle using a Compass** : Construct an equilateral triangle and another equilateral triangle on the side of the constructed one.

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