You can't get an actual number because, with a right triangle (90 degree), Pascal's formula is:
base^2 + height^2 = hypotenuse^2
base^2 + height^2 = 83^2
base^2 + height^2 = 6889
base^2 = 6889 - height^2
base = sqrt(6889 - height^2)
For the base you get a formula in terms of height. This means you can't get an actual number for the base without knowing the height.