Answer:
C. √2 - 1
Step-by-step explanation:
If we draw a square from the center of the large circle to the center of one of the small circles, we can see that the sides of the square are equal to the radius of the small circle (see attached diagram)
Let r = the radius of the small circle
Using Pythagoras' Theorem 
(where a and b are the legs, and c is the hypotenuse, of a right triangle)
to find the diagonal of the square:



So the diagonal of the square = 
We are told that the radius of the large circle is 1:
⇒ Diagonal of square + r = 1





Using the quadratic formula to calculate r:




As distance is positive,
only
The numerator could be written a⁴/⁵
The denominator could be written a²/³
Now solve ( a⁴/⁵) / (a²/³) ==> a⁽⁴/⁵ ⁻²/³) = a⁽²/¹⁵)
This is the simplest way
Andrew is wanting to build a slide for his daughter's tree house in the backyard. The tree house is approximately 5 feet off the ground and he wants the slide to have a 30 degree angle with the ground. He will need to by 10 ft of sliding board.