Draw a number line and take a point Q at 2 such that l(OQ) = 2 units.
Draw a line QR perpendicular to the number line through the point Q such that l(QR) = 1 unit. Draw seg g OR.
∆OQR formed is a right angled triangle. By Pythagoras theorem,
[l(OR)]2 = [l(OQ)]2 + [l(QR)]2
= 22 + 12
= 4 + 1
= 5
∴l(OR) = √5 units
…[Taking square root of both sides]
Draw an arc with centre O and radius OR. Mark the point of intersection of the number line and arc as C. The point C shows the number √5.