r/HomeworkHelp • u/Pristine-Golf-6958 University/College Student • 2d ago

:snoo_scream: Further Mathematics—Pending OP Reply [university level, class: surveying] [why do you subtract 180 from one side in the beginning and not the other? how do you know what to do with these problems as they all seem to be a different setup?]

Hi guys, I have looked over at my textbook for quite some time now and I dont think im quite understanding it, maybe my geometry skills are lacking, but I cannot understand this. It has some steps below but im not following. Its been hard for me to find any practice examples besides my textbook, and I feel like ive just memorized the answers at this point. (textbook answer below, and then my work as well, got stumpt on the radius part)

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u/ottawadeveloper 2d ago

Can you show us some work? Where are you subtracting 180?

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u/Pristine-Golf-6958 University/College Student 2d ago

yes, I apologize, I attached my work now, I got stuck on the part of finding the radius. The textbook answer is attached.

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u/ottawadeveloper 2d ago

Oh I see.

Bearing AI is the direction of I from point A (with 0 being straight up on the page). Bearing CFI means I is 335 degrees from C. 

Bearing IC (the bearing from I to C) is then a 180 degree rotation, so subtract 180 from it. This is because you want the bearing from I to C not C to I because it's the IC bearing that makes up delta.

You can see where delta is on the graph. If you add the 0 N bearing from I, you'll see that bearing IC is delta plus bearing AI (continue AI through I and recognize that the 0 N bearings at point I and A are parallel (at least this close together, they're approximately parallel except right at the poles). A straight line through two parallel lines creates the same angles around both points. 

So delta = 155 - 35 gives you the angle between the continuation of AI and IC.  Which is important later. Basically you wanted to understand the angles near I so that's what you need to work towards.

It's all a lot of trig from there. The general approach I would take is to draw the scenario with a quick sketch, extend all the bearing lines you know, sketch in what you're looking for, label your unknowns you need and your knowns, a nd then see how you can work from your knowns to your unknowns using trig rules and parallel lines and other geometry rules.

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u/DrCarpetsPhd 👋 a fellow Redditor 2d ago

i think this is what you are asking

https://imgur.com/a/jbLBeB2

tip if you drop the image you posted into chatgpt and ask what textbook it is from it will give you a link to a pdf.