I don't understand this. Can someone please help me!!!!

Question

In the figure: AB and AC  are tangent to circle S.

Find the measure of SB if AB = 10.5 and AS = 15. Round to two decimal places if necessary. 

Answer 1

Consider the right triangle ABS. AS is the hypotenuse.

AS = 15, and AB = 10.5

Thus,SB^2 - AB^2 = SB^2

SB^2 = 15^2 - 10.5^2

SB^2 = 114.75

SB = 3√51/2

Answer 2

A line that is tangent to a circle is perpendicular to the radius to that point.

Let r = the radius SB

Then r² + 10.5² = 15²

r² = 15² - 10.5²

r² = 114.75

r = 10.71