(5√2) squared: I know the answer is 50. But how do you arrive at this answer?

(5√2) squared=(5 squared)(√2 squared) = ...

Original expression:
(5√2)²

Distribute the square:
5² (√2)²
25 * 2
50

(5 x √2) squared
= 5 x√2 x 5 x√2
= 5 x 5 x √2 x √2 <---- because multiplication is commutative, i.e. you can change the order
= 25 x 2
= 50

It's the same as saying 5 squared * sqrt2 squared
5^2 is 25 and sqrt2^2 is 2
25*2 is 50