Question 264858
this is actually a triangle quaestion as the diagonal line is the hyponuse of the triangle. 
{{{A^2+B^2=C^2}}}
A=4
B=9
find C
{{{4^2+9^2=C^2}}}
{{{16+81=C^2}}}
{{{97=C^2}}}
{{{sqrt(97)=sqrt(C^2)}}}
{{{9.8488=C}}} or {{{sqrt(97)=C)
Round to the tenth
{{{9.8=C}}} the diagonal 9.8 inches long

check answer:
{{{A^2+B^2=C^2}}}
{{{4^2+9^2=(sqrt(97))^2}}}
{{{16+81=97}}}
{{{97=97}}}