This is a square means ithas all sides equal Let say side is x And diagonal length is given 5 U know something is called pythagorean thoeram Which says relationship between sides of a right triangle Square has right triangle each side So hypotenuse^2=lenghth^2+base^2 Here hypotenuse is diagonal which is given 5 So 5^2=x^2+x^2 25=2x^2 x^2=12.5 x=√12.5=2.5√2 Answer is A
