The answer is: [A]: " 3 √2 " .
_______________________________
Solve for "s" ;
s² + s² = 6² ;
2s² = 36 ;
__________________________________
Divide EACH side of the equation by "2" ;
__________________________________
2s² / 2 = 36 / 2 ;
to get:
__________________________________
s² = 18 ;
__________________________________
Take the positive square root of EACH side:
__________________________________
√(s²) = √(18)
__________________________________
s = √(18) = √9 * √2 = 3 √2 ; which is: Answer choice: [A].
_________________________________________