Hey!!!
Answer is....
diagonals of square bisect each other at right angles.
let diagonal be 2x
Using Pythagoras in a triangle enclosed by a side and 2 half diagonals...




side of a diagonal=2 sqrt50

cm......
HOPE IT HELPS YOU '_'
That's for the equation I got from the picture
If you want to round 49.39 to the nearest tenths place you will have to look at your tenths digit.
The digit is 3, right?
Look at the next number after 3. It is the number 9 for the hundredths place. If the number is bigger than 5 you round it. If it is smaller, you keep it the same. 9 is bigger than 5 so you make the 3 into a 4.
Then, you're answer is 49.4 or 49.40 (Which are basically the same answer)
It also works the same with the other digits. Simple, right? :)