tv-sets are rated by the screen size and the screen size comes from the length of its diagonal.
so a 57" TV has a 57" diagonal.
Check the picture below.
[tex]\bf \stackrel{length}{4\left( \cfrac{57}{5} \right)}\implies \cfrac{228}{5}\implies 45\frac{3}{5}~\hfill \stackrel{width}{3\left( \cfrac{57}{5} \right)}\implies \cfrac{171}{5}\implies 34\frac{1}{5} \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ \stackrel{Area}{\cfrac{228}{5}\cdot \cfrac{171}{5}}\implies \cfrac{38988}{25}\implies 1559\frac{13}{25}[/tex]
