Question 639379
The sprinkling radius will have to be half the length of the diagonal of the square garden.

Garden is a square
The diagonal and the sides of square form a right triangle.
so the diagonal is the hypotenuse with the sides as the other two sides of a right triangle

let the length of side of square be x

area = x*x = x^2
x^2= 841
x= sqrt(841) = 29
side = 29

Apply pythagoras theorem
diagonal ^2= 29^2+29^2
diagonal^2= 1682
diagonal = 41.01 

half the diagonal = 20.5 feet

The radius of the sprinkler