Question 44938
You have a 16:9 rectangle with a diagonal of 42"
The sides are in a ratio of 16x:9x

Using Pythagoras you have the following:
(16x^2) + (9x^2) = 42^2 
337x^2 = 1764
x^2= 5.234
x=2.878

Your length is 16x = 36.61 inches 
Your width is 9x=20.59 inches.

Cheers,
Stan H.