PQ is a radius. QS is tangent to the circle. In this scenario (a radius and a tangent passing through the same point of the radius) the two segments are always perpendicular.
This implies that PQS is a right triangle. We know that PQ = 10 because it's a radius.
Also, we have
because PR is a radius and RS is given.
So, we can derive QS using the pythagorean theorem:
When you multiply a base with an exponent by a base with an exponent, you add the exponents together. (But you can only combine the exponents when the bases are the same)
For example:
(they have the same base of x)
(you can't combine the exponents because they have different bases of y and x)
When you have a negative exponent, you move the base with the negative exponent to the other side of the fraction to make the exponent positive.
For example:
or
or
Add the exponents together
Make the exponent positive
Simplify