Kinda Urgent 3d Trig word problem. Need help. Exam on monday...! (1 Viewer)

[S1M0]

Alright guys, its kinda urgent...but i need help. Please, PLEASE help.

Here's the question:

David walks along a straight road. At one point he notices a towar on a bearing of 053 Degrees, with an angle of elevation of 21 Degrees. After walking 230m, the tower is on a bearing of 342 degrees, with an angle of elevation of 26. Find the height of the tower to the nearest metre.

Can't seem to get the right answer. Please help, a diagram would be MUCH appreciated. Thankyou

 

[S1M0]

Bump.

Comon........

 

[ianc]

hi there! i am not sure whether or not I have got the right answer, please check.....although even if it is wrong, the diagram part is definitely correct and I have just stuffed up the algebra somewhere along the way

hope this helps!

edit: just noticed that you dont need the sine rule for that first part, all you need to do is use the simple trig ratio tan(x)=opposite/adjacent....oh well you get the idea

with 3D trig, the challenge is in the diagram, once you get it out the actual trig is fairly straightforward

 

[S1M0]

Answer's 84m. But your diagram's just perfect...which helps a lot, i think i can see where i went wrong.

Yeah thanks a lot. Must've took you a long time to draw that diagram, so i appreciate it and everything.

 

[S1M0]

i managed to get 48m, by making AB = tan64 x h and y = tan69 x h. Then i used cos rule, and managed to sub for h.

But the damn answer's 84m.....

 

[vafa]

what software do you use for drawing diagrams and typing mathematical equations?

 

[S1M0]

what software do you use for drawing diagrams and typing mathematical equations?

If you're talking to me, i don't use any.

 

[vafa]

not, you.
I meant ianc.
sorry about that.

 

[Evergreen]

sorry if the image looks shit. i was in a rush lol.

btw for this quesiton i only used sine rule. But i think there is another way with cosine.

on the left d/sin26= 189.262/sin90

d= 84m~

 

[S1M0]

sorry if the image looks shit. i was in a rush lol.

btw for this quesiton i only used sine rule. But i think there is another way with cosine.

on the left d/sin26= 189.262/sin90

d= 84m~

How on earth did you manage to get for your measurements in the sine rule, the measurements, Sin 133 and Sin 37?????

I dont get the ones in bold, how you managed to get those angle measurements...

 

[Evergreen]

133= 69+64
37=21+16

 

[S1M0]

133= 69+64
37=21+16

Thanks a lot.

Edit: Damn, that was so simple! I'm almost embarassed that i had to ask you how you came up with those measurements.

 

[Evergreen]

yeh just keep your calculations simple. dont overthink it.

 

[ianc]

thanks for the compliments - yeah i used microsoft visio for the pictures, which is a very nice tool, and then maple for the number crunching.


and by the way my method for solving this question was correct - i realised that i forgot maple does trig using radians, and i had simply entered in the numbers thinking they were degrees......how stupid!

another great tool for typesetting maths which i am just getting my head around is LaTeX - it's a really intuitive language that produces really nice output, and best of all its free! any math equations that you see on wikipedia are created using the LaTeX engine


have a good one!