Question 31148
the square has sides x and the diagonal of the square is 2r 
therefore the triangle formed by the diagonal and the two sides x is
x~2+x~2=(2r)~2 or 2x~2=(2r)~2 or 2x~2=4r~2 or x~2=2r~2 or x=sqrt of 2r~2
or x=r sqrt of 2