O is the centre of circle and tangents from point A and B are parallel
We know that the line joining point of contacts of two parallel tangents (here AB) passes through the centre
And as a line from the centre is perpendicular to tangent, hence that line(AB) will be the distance between parallel tangents
AB passes through centre O hence AB is also the diameter of the circle
Hence the distance between the two parallel tangents will be the diameter of the circle
Radius is given 10 cm
Hence diameter of circle = 2 × radius
Hence AB = 2 × 10
⇒ AB = 20 cm
Hence distance between parallel tangents is 20 cm
