Use pythagoras theorem, a²+b²=c², where c is the hypotenuse, and a and b are the smaller sides.
Therefore, (2√2)²-(√6)²=x²
therefore, square rooting both sides, noting that the square root, which is usually ±, is only positive since it's a length, x = √2
and (√10)²+(√17)²=x²
x=√27