1] Draw number line and take a point O representing O on it.
Take a point A on the number line such that OA = 1(units)
2] Take a point B on the number line such that AB = 2(units)
3] With centre B draw a right angled triangle ABC(right angled at A) such that AB =2 and BC =1
4] With A as centre and radius AC draw an arch that cuts the number line at P
5] Then, AB = AP = √5
6] OC =OA+AP=1+√5.