i want to buy a tv set, but the entertainment center i have is 30 inches by 40 inches, what is the largest tv set i can buy
TV sets are measured according to their diagonal distance from one corner to the opposite. Therefore, I feel as though for this question it's simply asking you to find the distance from the one corner to the opposite. To do this you want to view this as a triangle rather than a square and you want to find the hypotenuse.
Recall: a^2 + b^2 = c^2
with a and b being the 2 sides and c being the hypotenuse.
30^2 + 40^2 = c^2
900 + 1600 = c^2
2500 = c^2
square root of 2500 = c
50 = c
Therefore the largest TV set you could buy is a 50 inch!