Basic Trigonometry Problem

tntcoder

tntcoder

tntcoder

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7 Apr 2004
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Hey guys,

Just going over an old exam paper, and theres a basic trig question which i really cant remember how to do, basically just working out the length of a side and an angle :rolleyes:

trigml3.jpg


I was given the 2 sides, and the 28 degrees angle. I worked out the other angle by 90 - 45 = 17 degrees, which i think is correct? Then as you can see I used both Pythagoras and trig to work out the side a, which didn't work as they both give different values. Any ideas on what ive done wrong :rolleyes:

Thanks
Jack
 
Ummm yup!

Unless I have gone senile the internal angles of a triangle add up to 180.

So your other angle should be 62 degrees!

Your trig might work a bit better then!
 
Beren said:
Ummm yup!

Unless I have gone senile the internal angles of a triangle add up to 180.

So your other angle should be 62 degrees!

Your trig might work a bit better then!
Click to expand...
That's what I was thinking.

Which internal angle were you given? One of them is wrong.
 
Exactly.. 28 + 17 /= 90..

You sure the 28 degree angle is right?

cos-1( a/h) = cos-1(4/7) = 55degrees.. (what you said was 28).

So you must have something wrong
 
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When I read this i thought it was GCSE or something but no the guy is 20 :eek:

KaHn

George, as he said he was given the 28 and a right angle triangle (as far as i can make from his post) so the other angle is 180-90-28 = 62.

If this is not the case and he has the 28 and 17 angle given he will have to use other trig idents to get the right angle, gimme a sec and ill see if I have them here.
 
! i did this at GCSE, but there is a maths module i have had to do for my first year of uni. I havnt done this stuff for a few years.

I still cant see why the pythag and trig give different results, when using the given angle of 28 in sin.
 
tntcoder said:
! i did this at GCSE, but there is a maths module i have had to do for my first year of uni. I havnt done this stuff for a few years.

I still cant see why the pythag and trig give different results, when using the given angle of 28 in sin.
Click to expand...

Trig and the sin ident you are using only work for right angle triangles, so if you are using the 2 angles 28 and 17 you do not have a right angle triangle!

KaHn
 
That triangle doesn't work at all...

If the two sides are right then the angles are 55 and 35... and the other side is 5.7

Bah beaten to it by georges...

That question is nonsense I'm afraid!
:edit: TNT - Is it actually a right angle triangle? 1st year maths should be a long way past basic trig!
 
KaHn said:
When I read this i thought it was GCSE or something but no the guy is 20 :eek:

KaHn

George, as he said he was given the 28 and a right angle triangle (as far as i can make from his post) so the other angle is 180-90-28 = 62.

If this is not the case and he has the 28 and 17 angle given he will have to use other trig idents to get the right angle, gimme a sec and ill see if I have them here.
Click to expand...


Yeah, but he said it was a right angled triangle, and the 28 degree angle does not work with those values in a right angle.
 
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