3d Trig (1 Viewer)

[clever angel]

hi ppl,

i am having a hard time doing 3d trig. Does ne know a simpler way of solving problems on 3d trig ? plzzzzzzzzzz help !!!!!!!!!!!!

 

[zahid]

You need to be more specific. Different questions require different approaches.

You need to do the following

1. Know you Sine and Cosine rules
2. Know your bearings
3. Draw a diagram with the given information.

Thats it.

 

[Slidey]

You also need to do one more thing:

4. Not draw the wrong diagram.

 

[withoutaface]

3D trig is deductive thinking, similar to that required for circle geo, but less challenging.

5. Remember sine rule doesn't work for angles >90'

 

[withoutaface]

You also need to do one more thing:

4. Not draw the wrong diagram.

In the HSC you will be given a diagram. The board made the mistake of not doing that one year and the markers for that section were stuck for weeks longer than the rest.

 

[Slidey]

5. Remember sine rule doesn't work for angles >90'

How do you figure that? Let me show you:

OK. Two ways. The second one is dodgier because I don't know what the circle geo theorems I used are called. Ah well, if you know circle geo, take a look at it. Although maybe you shouldn't because it has to do with the triangle circumscribing a circle of radius R, where 2R is the ratio of sides to their corresponding angles - the sine rule.

 

[Xayma]

3D trig is deductive thinking, similar to that required for circle geo, but less challenging.

5. Remember sine rule doesn't work for angles >90'

Yes it does.

You just have to remember that multiple answers can occur if the &sum; of &ang;'s in the &Delta; can equal <180&deg; (with the other angle filling in the unknown).

This was the case for a HSC question a few years back.

 

[acmilan]

Yeh sine rule can be used but you have to be careful with it.

 

[withoutaface]

Yeh sine rule can be used but you have to be careful with it.

Hence it's better to avoid it altogether in such situations and use cosine rule.

 

[Xayma]

Except in such situations where the cosine rule does not work. Such as you have 1 angle and 2 sides (the angle being across from one of the known sides).

 

[withoutaface]

Yeah and you can use the sine rule with then <90' angles to find those sides.

 

[Xayma]

But sometimes it also works for angle >90&deg; and you must include the other answer if it works.

 

[...]

let just make love with sin and cosin

 

[Mr. Osama]

let just make love with sin and cosin

oooook then.

 

[wrong_turn]

sine rule would be the easiest of the two to remember imo. however, you have to know both cosine and sine rule tro work at questions. though in 3d trig, your most likely gonna have to use cosine rule rather than sine rule.

so make sure if you are weak at the cosine rule, practice some questions. it does not neccesarily have to be year 12 level. just get familiar with it, within the year 10 advanced textbook. they're much similar. or else the fitzpatrick 2-unit book.