Question 281766
The area of a square has a formula: {{{A = s^2}}}

we have:

{{{64 = s^2}}}
=>{{{s = 8}}} given it must be positive since we are talking about length


The length of a diagonal would make a triangle and from there you can use the Pythagorean theorem.

Where we have: {{{8^2 + 8^2 = (diagonal)^2}}}
=> {{{sqrt(64 + 64)=diagonal}}}
=> {{{sqrt(128) = diagonal}}}
=> {{{highlight(8 * sqrt(2)) = diagonal}}}