Hello from MrBillDoesMath!
Answer:
sqrt(105)
(which is approximately 10.25 centimeters )
Discussion:
Call the unknown leg"a". From the Pythagorean theorem
8^2 + a^2 = 13^2 => subtract 8^2 = 64 from both sides
a^2 = 13^2 - 64 => as 13^2 = 169
a^2 = 169 - 64 = 105 => take the square root of both sides
a = sqrt(105) which is approximately 10.25 centimeters
Thank you,
MrB