To find a third whole number that forms a Pythagorean triple with 13 and 85, we can use the formula for generating Pythagorean triples:
a = m^2 - n^2
b = 2mn
c = m^2 + n^2
where a, b, and c are the three sides of a right triangle, and m and n are positive integers with m > n.
We know that 13 and 85 are already two sides of a right triangle, so we can use the Pythagorean theorem to find the third side:
c^2 = 85^2 + 13^2
c^2 = 7226
c ≈ 85.0
So the third number that forms a Pythagorean triple with 13 and 85 is approximately 85.