for a right triangle with legs legnth a and b and hypotonuse c a²+b²=c²
so the legs are 7 and the diagonal is c a=b since all 4 sides of a square are equal legnth 7²+7²=c² 49+49=c² 98=c² sqrt both sides √98=c (√49)(√2)=c (7)(√2)=c 7√2=c
the legnth of the diagonal is 7√2 inches or aprox 9.899 inches