Draw ∠AOB = 80° and with any radius and A as center draw an arc.
With X as center and radius more than half of XY draw an arc and with Y as center and equal radius draw an arc and let the arcs intersect at C.
∠COB is equal to 40°.
With Y as center and radius more than half of PY draw an arc and with P as center and equal radius draw an arc and let the arcs intersect at D.
∠DOB is 60°.
With O as center and OX as radius extend the Arc XY to Arc XY’.
With Q as center and XQ as radius, draw an arc which cuts the Arc XY’ at R.
∠ROB is 120°.
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