Tangents drawn from an external point to a circle are equal in length. In this case, SA and SB are tangents from point S.
Given SA = 12 cm, therefore SB must also be 12 cm.
So, SA = SB = 12 cm.
Consider the triangle formed by the external point S and the points of tangency A and B, which is triangle ASB.
We know that SA = SB, making triangle ASB an isosceles triangle.
We are given that the angle between the tangents, angle ASB, is 60°.
An isosceles triangle with the angle between the equal sides being 60° is always an equilateral triangle.
In an equilateral triangle, all sides are equal in length.
Therefore, the length of the chord AB is equal to the lengths of the tangents SA and SB.
AB = SA = SB
AB = 12 cm
In the given figure, DE is tangent to the circle at a point B. $\Delta \text{ABC}$ is constructed such that A and C are points on the circumference of the given circle, with $\text{AB} = \text{AC}$. If $\angle \text{ABD} = 65^\circ$, then what is $\angle \text{BAC}$? (Figure is not to scale)

In the given circle, diameter AB is extended to meet chord CD extended at P. If the lengths of the line segments AP, CP and DP are 12 cm, 8 cm and 6 cm, respectively, what is the length of the radius of the circle?

There are two concentric circles. The radii of the two circles are 100 m and 110 m respectively. A wheel of radius 30 cm rolls on the smaller circle and another wheel rolls on the larger circle. After they have completed one revolution, it is found that the two wheels rolled equal number of times
on their respective axes. What is the radius of the other wheel ?