Answer:
Remember that if u draw a line in the middle your square will form two triangles.
The line u forming will be your diagonal.
Then u use the Theorem of Pythagoras as the diagonal in the middle forms two right angle triangles.
Then it's going to be 4 squared plus 4 squared Then your answer you square root it.
Since it's from corner to centre you will take your answer and divide it by 2.As your answer will be 2 square root 2.