Please help me with this equation below.

a) We have an aspect ratio of 4:3

This means that the width of the screen, W, is about 4/3 times the height of the screen, H.

Then we have the equation:

W = (4/3)*H

And the diagonal of a rectangle with width W and height H is:

D = √(W^2 + H^2)

Then if we have a 15 in TV, then we have D = 15 in.

Then we have:

15 in = √(W^2 + H^2)

Now we can use the relation W = (4/3)*H and replace this in the above equation:

15 in = √(((4/3)*H)^2 + H^2)

Now we can solve this for H:

15in = √( (16/9)*H^2 + H^2)

(15in)^2 = (16/9)*H^2 + (9/9)*H^2 = (25/9)*H^2

(9/25)*(15in)^2 = H^2

√( (9/25)*(15in)^2) = H

(3/5)*(15in) = H = 9 in

The height is 9 inches, and the width will be:

W = (4/3)*9in = 12in.

Now let's do the same for a 42 in tv.

We can use the same equation than before, this time we get:

42 in = √(((4/3)*H)^2 + H^2)

We can do the exact same procedure as before, and we will get:

(3/5)*(42in) = H = 25.2 in

Then the width is

W = (4/3)*H = (4/3)*25.2in = 33.6 in

b) Now we do the same, but now we have the relation:

W = (16/9)*H

Then if D is the diagonal, we have the equation:

D = √(W^2 + H^2) = √( ((16/9)*H)^2 + H^2)

This time we can simplify it for any general D.

D^2 = (16/9)^2*H^2 + H^2

D^2 = (256/81)*H^2 + H^2 = (256/81)*H^2 + (81/81)*H^2

D^2 = (337/81)*H^2

(81/337)*D^2 = H^2

√( (81/337)*D^2) = H

(9/18.36)*D = H

Then if we have a 42 in TV, the height is:

(9/18.36)*42in = H = 20.59 in

And the width will be:

W = (16/9)*H = (16/9)*20.59in = 36.60 in

If we have a 60 in TV, we get:

(9/18.36)*60in = H = 29.41 in

And the width will be:

W = (16/9)*H = (16/9)*29.41in = 52.29 in

c) if all the aspect ratios are always exactly 16:9, then no, the width and height should be exactly the same for all the TV with that ratio.

2 is the final ! : )