Draw a circle of radius 4 cm with centre O. draw a diameter POQ. through P draw a tangent to the circle.

STEPS OF THE CONSTRUCTION;

Step 1: Take a point O on the plane of the paper and draw a circle of radius OP = 4 cm.

Step 2: extend PO , let it cuts the circle at point Q. POQ is the diameter.

Step 3: Construct ∠QPT = 90°. extend TP.

Here, T'PT is the required tangent to the circle at P.  (Radius is perpendicular to the tangent at point of contact)