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We need to draw a triangle ABC with ∠ABC = 120°

⇒ ∠B = 120°

Since we are given only one angle to draw a triangle we need to assume the other two angles of a triangle.

It is impossible to draw a triangle with only one angle.

∠A + ∠B + ∠C = 180°

∠A + ∠C = 60°

Let’s assume ∠A as 30° and ∠C as 30°

1. Let us take AB as base of the triangle.

2. So, draw a line segment and name it as AB (Here length is not specified so we can assume that also.)

3. Place the protractor at B and draw a ray with 120°

4. Place the protractor at A and draw a ray with 30°

5. 2 Rays will intercept at some point and name that point as C

6. Thus, we have drawn a triangle with ∠ABC = 120°.