Assuming a and b are the legs and x is hypotenuse of a right triangle we have:

a^2 + b^2 = c^2 (Pythagorean Theorem)

c = square root 9 

c = 3

b = square root 4

b = 2

Plug c = 3 and b = 2 into a^2 + b^2 = c^2:

a^2 + 2^2 = 3^2

a^2 + 4 = 9

a^2 = 9 - 4

a^2 = 5

a = 2.24

We need to ignore the negative solution since the length can only be positive.