Draw a circle of radius 6 cm. From a point 10 cm away from its centre, construct the pair of tangents to the circle and measure their lengths.

Step 1: Construct a circle with radius=6 cm and centre be C.
Step 2: With the help of a scale, locate a point A which is 10 cm from C.
Step 3: Now, draw the perpendicular bisector of the line joining points C and A. Let it be at point M.
Step 4: Now draw another circle with centre at M and radius=5 cm=(CA/2) and lets say this circle cuts the previous circle at points N and Q.
Step 5: Draw the lines AQ and AN which are our external tangents.
Since, △CQA is right angle triangle at ∠Q
CA=90∘
Therefore using Pythagoras theorem,
(CQ)²+(AQ)²=(CA)²
⇒(10)²-(6)²=(AQ)²
QA=8 cm is the length of the tangent.