Question 258963
This depends on the Pythagorean theorem about right triangles.
a and b are the legs (sides of the TV)  and c is the diagonal ( the hypotenuse)
a^2+b^2=c^2
where a=15 and c=19
15^2+b^2=19^2
225+b^2=361
136=b^2
11.66=c
We are not interested in negative roots since we can't have a negative side to the TV
11.66 is closest to 12 inches.