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Trigonometry in 3D - planes

Hello, I can mostly understand trigonometry in 3D except when it involves 'planes'. I don't understand which angles I need to find out and why? If someone could please explain to me which angles in the attatched images I need to calculate, I'd be very grateful!

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Reply 1

TenOfThem

CAG

and

VME

where M is the mid pt of AB

Reply 2

TheWantedGuy

Original post by TenOfThem

CAG

and

VME

where M is the mid pt of AB

I don't understand where you mean by VME, and could you explain why it's these angles. I always get confused when it involves planes.

Reply 3

TenOfThem

VME is the angle between the lines VM and ME

The angle between planes is always at the mid point of their joining edge

Reply 4

TenOfThem

Original post by TheWantedGuy

I don't understand where you mean by VME, and could you explain why it's these angles. I always get confused when it involves planes.

for CAG you need to drop a perpendicular from the line to the plane

But that already exists here .. GC

Reply 5

TheWantedGuy

Original post by TenOfThem

VME is the angle between the lines VM and ME

The angle between planes is always at the mid point of their joining edge

But how do I know the joining edge of the following planes:

Reply 6

TenOfThem

Original post by TheWantedGuy

But how do I know the joining edge of the following planes:

The edge they have in common

The 2 letters they share in their descriptions

Reply 7

TheWantedGuy

Original post by TenOfThem

The edge they have in common

The 2 letters they share in their descriptions

Oh that makes sense. How about if it is a line and a plane as in the first example, why use that angle?

Reply 8

TenOfThem

Original post by TheWantedGuy

Oh that makes sense. How about if it is a line and a plane as in the first example, why use that angle?

post 5

Reply 9

TheWantedGuy

Original post by TenOfThem

post 5

Can I not use the triangle in:

since it involves the line AG and plane ABCD and a perpendicular?

Reply 10

TenOfThem

Original post by TheWantedGuy

Can I not use the triangle in:

since it involves the line AG and plane ABCD and a perpendicular?

That was what I said

CAG

Reply 11

TheWantedGuy

Original post by TenOfThem

That was what I said

CAG

Sorry I meant the triangle I drew in with red.

Reply 12

TenOfThem

Original post by TheWantedGuy

Sorry I meant the triangle I drew in with red.

That triangle does not exist

Reply 13

TheWantedGuy

Original post by TenOfThem

That triangle does not exist

http://postimage.org/image/jflzihrgn/ how about now?

Reply 14

TenOfThem

Original post by TheWantedGuy

http://postimage.org/image/jflzihrgn/ how about now?

I can see where you have drawn red

That is not a triangle

Reply 15

TheWantedGuy

Original post by TenOfThem

I can see where you have drawn red

That is not a triangle

Oh why not? lol

Reply 16

TenOfThem

Original post by TheWantedGuy

Oh why not? lol

well ... if we pretend it does exist and call it DAM

Where is M?

Reply 17

TheWantedGuy

Original post by TenOfThem

well ... if we pretend it does exist and call it DAM

Where is M?

Was assuming it would be the midpoint, so half of 12.3, but I can see that's wrong now. Yet, I still don't understand why you chose CAG? What do you need to look for when there is a line and plane and you need to find the angle?

Reply 18

TenOfThem

Original post by TheWantedGuy

You need the line AG

And you need a perpendicular from the line to the plane GC

Then you need to complete the triangle and find the angle at A ... where the line meets the plane

Reply 19

TheWantedGuy

Original post by TenOfThem

You need the line AG

And you need a perpendicular from the line to the plane GC

Then you need to complete the triangle and find the angle at A ... where the line meets the plane