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Old 31st May 2020, 07:49   #1
macafee2
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Default Help reqd with angels and Zeus

I need some help please working out angles and using my oh so very old Zeus book. It has been so long since I used if for angles I have forgotten how.

Please see this diagram taken from the internet.

what is angle A and B?

I know a and b.
using a squared plus b squared I can work out c
a = 24, b = 96, so I reckon c = 98.955 rounding to 3 decimal places

my Zeus book says :
data known b & c
Tan B = b/c
96 divided by 98.955 = 0.97

This is where I am a bit lost.
I think my Zeus book on a page that is titled Table of Natural Tangents has 0.97132 but I am unsure of the angle. Is the angle 44 point something?
What is the something?

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Old 31st May 2020, 10:26   #2
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For things like this, I don't even bother with calculating. Had to do a lot of it at school and college so it's nice to simply use the internet! I think I'd struggle to calculate it without practice now. If you type in triangle calculator there are websites that work it all out for you. You only need three figures.

Your triangle is near enough a right angled triangle, and results are as follows




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Old 31st May 2020, 11:19   #3
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mm now thinking about my 44 degrees its way out, idiot.

14 degrees, thank you.
No idea on your working out as I don't have a clue

Still no idea how to use my Zeus book

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Old 31st May 2020, 12:36   #4
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Didn't work any out! Just typed the lengths into a website that calculates it all out.
You can only calculate the angles of a right angled triangle when you know the length of at least two sides. If the triangle isn't a right angled triangle you wouldn't be able to calculate the unknown length using a2 + b2 = c2. You would have to make a right angled triangle and calculate the lengths and angles out. For that you'd use sohcahtoa

Sine of opposite / hypotenuse
Cosine of adjacent / hypotenuse
Tangent of opposite / adjacent

So if you take the triangle in my post above and we wanted to calculate the angle B we would need to calculate the cosine of the adjacent length divided by the hypotenuse

96/98.955 = 0.97

Then you'd look up the cosine of 0.97 in the tables and you'll find it's 14. So that's your angle.

Then because you know it's a right angled triangle 180 - 90 - 14 = 76 which is near enough.

But remember, it's only works with right angled triangles!!!

If it's not a right angled triangle, there are lots of other ways to calculate. But in any case you need three lots of data. If you've only got two lengths you can't work anything else out. You can't even calculate the third length because you need at least one angle. So don't take that above as accurate because your triangle may not be right angled.
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Old 31st May 2020, 14:07   #5
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Reading these posts takes me back 60yrs to my school days. Still not got a clue what your talking about.
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Old 31st May 2020, 14:54   #6
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Quote:
Originally Posted by rrobson View Post
Didn't work any out! Just typed the lengths into a website that calculates it all out.
You can only calculate the angles of a right angled triangle when you know the length of at least two sides. If the triangle isn't a right angled triangle you wouldn't be able to calculate the unknown length using a2 + b2 = c2. You would have to make a right angled triangle and calculate the lengths and angles out. For that you'd use sohcahtoa

Sine of opposite / hypotenuse
Cosine of adjacent / hypotenuse
Tangent of opposite / adjacent

So if you take the triangle in my post above and we wanted to calculate the angle B we would need to calculate the cosine of the adjacent length divided by the hypotenuse

96/98.955 = 0.97

Then you'd look up the cosine of 0.97 in the tables and you'll find it's 14. So that's your angle.

Then because you know it's a right angled triangle 180 - 90 - 14 = 76 which is near enough.

But remember, it's only works with right angled triangles!!!

If it's not a right angled triangle, there are lots of other ways to calculate. But in any case you need three lots of data. If you've only got two lengths you can't work anything else out. You can't even calculate the third length because you need at least one angle. So don't take that above as accurate because your triangle may not be right angled.
I did a web search and I cant find a web page I understand telling me what the cosine of 0.97 is. What web site did you use?

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Old 31st May 2020, 16:02   #7
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This is the first image off google



Just read off the decimal numbers and it gives you the equivalent angle in degrees on the left

14 degrees is exactly 0.9703, but to two decimal places obviously is 0.97 therefore near as 14 degrees

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Last edited by rrobson; 31st May 2020 at 16:08..
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Old 31st May 2020, 17:25   #8
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Quote:
Originally Posted by rrobson View Post
This is the first image off google



Just read off the decimal numbers and it gives you the equivalent angle in degrees on the left

14 degrees is exactly 0.9703, but to two decimal places obviously is 0.97 therefore near as 14 degrees

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AARRRRGGGG my search criteria was wrong, is was putting in something like what is the angle of cosine 0.97.

thank you rrobson

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Old 31st May 2020, 17:47   #9
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You mixed up the lengths for a , b & c . in your diagram . "c " cannot be 24mm, if "b " is 96
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Old 31st May 2020, 20:00   #10
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Quote:
Originally Posted by RoverP480 View Post
You mixed up the lengths for a , b & c . in your diagram . "c " cannot be 24mm, if "b " is 96
oh pooh you are right, it is b and c I know, sorry.


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