I have the below measurements.

Diagonal at 150 inches, (at 4:3 screen ratio), gives a width of 3.04 metres. (bottom left pic). (note 16:9 ratio at the same width of 3.04 metres, gives 138 inches diagonal, bottom right pic).

If I had a diagonal of 120 inches, what would the width be (still at 4:3 screen size ratio). What would the diagonal be given this resultant width, at 16:9 screen ratio?

Hope you’re good with sums. :)

All the shapes with the reduced diagonal are similar, so just factor all your 150” diagonal measurements by 120/150 = 4/5 = 0.8

The Rev Dodgson said:

All the shapes with the reduced diagonal are similar, so just factor all your 150” diagonal measurements by 120/150 = 4/5 = 0.8

Let’s see if I understand the question.

4:3 ratio gives a Pythagorean 3:4:5 triangle.
Diagonal 150 inches = 3.81 metres
gives width (4/5)*150 = 120 inches = 3.04 metres
and height (3/5)*150 = 90 inches = 2.28 metres
16:9 ratio then gives a height of (9/16)*120 = 67.5 inches = 1.71 metres
and a diagonal of sqrt(120^2+67.5^2) = 137.7 inches = 3.50 metres
That’s a match.

Reducing the diagonal from 150 to 120 inches, all dimensions shrink by a factor of 120/150 = 0.8.
So the diagonal at 16:9 screen ratio is 0.8*137.7 = 110 inches = 2.80 metres.

ie. What Rev Dodgson said.

So if the 120” diagonal is 80% of 150”. ( screen ratio of 4:3) width 3.04 metres.

then the width of 120” diagonal (screen ration 4:3) would be 80% of 3.04 metres = 2.43 metres.

Does this also apply for the 16:9 ratio?

ie. 138” (at ratio 16:9) would also be reduced to 80%? ie 110.4 inches diagonal.

Ya see…… the 150” @ 3.04 metres is too big to fit on the wall.

So there is this one 120 inches but it does not give the WIDTH of the screen.

So I need to know the WIDTH of the 120” screen (if the 120 inches is 4:3 screen ratio diagonal.)

So it’s all just simple % reduction (80%) all over for ALL dimensions in that pic? Or is there triggernometree involved with cos and sin and stuff.

Undunstumble?

Woodie said:

So if the 120” diagonal is 80% of 150”. ( screen ratio of 4:3) width 3.04 metres.

then the width of 120” diagonal (screen ration 4:3) would be 80% of 3.04 metres = 2.43 metres.

Look what I found. Seems to concur with sums.

100-inch screen, measured diagonally; 203 × 152 cm (width x height)
120-inch screen, measured diagonally; 244 x 183 cm (width x height) ————> This one.
150-inch screen, measured diagonally; 305 × 228 cm (width x height)

Bugger….. this one says “no it’s not” to the sums.

Woodie said:

Bugger….. this one says “no it’s not” to the sums.

They’ve got something wron there.

a^2 = b^2 +c^2

b= 2000mm,
c=1500mm,
Therefore:
a=98.425 inches.

Woodie said:

Bugger….. this one says “no it’s not” to the sums.

A right-angled triangle is A^2^+B^2^ = C^2^ with C being the hypotenuse….. is that right?

If that is the case, then the above is WRONG.

If that screen is 2 metres by 1.5 meters, then the diaganogonal would be just 98 inches? (or approx 100 inches). not 120 inches.

Oh dear….. methinks Mr Ebay site needs to get his pics right.

100 inches = 2 metres * 1.5 metres.
AND 120 inches = 2 metres * 1.5 metres

Woodie said:

Oh dear….. methinks Mr Ebay site needs to get his pics right. Now I trust you can see my enpuzzlements.

100 inches = 2 metres * 1.5 metres.
AND 120 inches = 2 metres * 1.5 metres

and no….. I didn’t buy it from THAT one, but it’s the same item.

Tells ya wot… the screen better be 2.43 metres wide when it gets here, for the 120” one I bought, or it’s going back!

And that calc was based on the pic of the 150” one that said 3.04 metres wide. What if that pic was wrong too?

Isn’t there a therorum of a right angle triangle, that is A=3 and B = 4 then C must be 5? ie a 3,4,5 right angled triangle?

That’s why I wanted someone to do some proper sums, with a 120” hypotenuse of a right angled triangle, with the other two sides in the ratio of 4:3 to give me the length of the other two sides.

Woodie said:

Tells ya wot… the screen better be 2.43 metres wide when it gets here, for the 120” one I bought, or it’s going back!

And that calc was based on the pic of the 150” one that said 3.04 metres wide. What if that pic was wrong too?

Isn’t there a therorum of a right angle triangle, that is A=3 and B = 4 then C must be 5? ie a 3,4,5 right angled triangle?

That’s why I wanted someone to do some proper sums, with a 120” hypotenuse of a right angled triangle, with the other two sides in the ratio of 4:3 to give me the length of the other two sides.

The 3-4-5 triangle is a way of setting out a right angle. Say at a building site, or on a piece of wood. I’s one solution to the “squares” equation I gave earlier.

Pythagoras

Arts said:

Pythagoras

Pythagoras was a square.

Michael V said:

The 3-4-5 triangle is a way of setting out a right angle. Say at a building site, or on a piece of wood. I’s one solution to the “squares” equation I gave earlier.

Ya see, Mr V. You know where it’s gotta fit. Between that big beam that runs across the middle of the loungeroom and the wall. (where the old sheet was nailed up to) At 3.04 metres wide (150” diagonogonal) it’s too wide. I don’t want the 120” diaganogonal to be too small. If the 120” is 2.4 metres wide, it fits sorta just snug and nice.

Why was the sheet nailed up? Cause last time I looked at these things, these screens were $300 – $500. Get them for about $90 now.

Arts said:

Pythagoras

That’s just a load of Isosceles.

From you, up there:

120-inch screen, measured diagonally; 244 × 183 cm (width x height) ————> This one.

That seems correct.

————————————————————————————————————

Also, Arts was correct – it’s the Pythagorean theorem.

https://en.wikipedia.org/wiki/Pythagorean_theorem