The right angle triangle representing the given scenario is shown below.
From the triangle,
AB represents the height of the tree = one leg of the triangle
AC represents the length of the rope = hypotenuse of the triangle
AB = x represents the distance from the base of the tree = other leg of the triangle
We would find x by applying the pythagorean theorem which is expressed as
hypotenuse^2 = one leg^2 + other leg^2
By substituting these values into the equation, we have
10^2 = 8^2 + x^2
100 = 64 + x^2
Substracting 64 from both sides of the equation, we have
100 - 64 = 64 - 64 + x^2
36 = x^2
Taking square root of both sides,
x = 6
The rope should be 6 feet from the base