Okay. The whole thing looks like a right-angled triangle. In this situation we are finding out the hypotenuse, which is the longest side in a right-angled triangle and in this case it's the length of the tightrope.
To find the hypotenuse (the tightrope), we have to use 'pythagoras'. It's this rule which states that in any right-angled triangle, the hypotenuse squared is equal to the sum of the other two sides squared. >> h^2 = a^2 + b^2 (where h is the hypotenuse and a and b are the other two sides)
h^2 = (25 - 10)^2 + 36^2 ... pythag
h^2 = 15^2 + 36^2
h^2 = 225 + 1296 = 1521
h = √1521 = 39!
