the 3rd side cannot be longer than the sum of the other two sides. A < 50
the 3rd side cannot be smaller than the difference of the other two sides: A>10
10<A<50
The 3rd side is somewhere between 10 and 50. Without more information that's all you can know.
If it were a right triangle, then you could narrow it down more
if the 3rd side were the hypotenuse, then it would = square root of (400+900) = about 36
if 30 were the hypotenuse then the 3rd side would = square root of (900-400) = about 22.4
20 can't be the hypotenuse, as the hypotenuse is the longest side, so 3rd side is either 36 or 22.4
