3D Trigonometry question (1 Viewer)

[youngsky]

Question: AB is a vertical tower 30 metres high, C and D are points at the same level as its foot A. The point C is due south of the tower and D is due east of C. If the angles of elevation from C and D to the top of the tower are 16° and 11° respectively, find the bearing of D from the tower and the distance CD.

Hey guys, back with another question. I have an answer for this one but not sure if it's correct or not.

Please solve + show working out thanks

 

[Drongoski]

Are the answers:

CD = 113.46 m

Bearing = 132 deg 41 min ?

 

[HeroicPandas]

Are the answers:

CD = 113.46 m

Bearing = 132 deg 41 min ?

I got that as-well (using trig ratios)

 

[Drongoski]

Op wants the working out - Heroic - you are good at providing the diagrams.

 

[HeroicPandas]

How do i post up graphs from microsoft word/geogebra?

- very messy.... sorry! i rushed it in the morning lol

Use the diagram as a guide, think of trigonometric ratios (sine, cosine, tangent) while having a goal

 

[HeroicPandas]

- Some working out i did in the morning...

Last part says:

 

[youngsky]

Thanks, understood everything except the last part
Pythagoras' theorem worked anyway

 

[HeroicPandas]

Thanks, understood everything except the last part
Pythagoras' theorem worked anyway

Aim: Find CD

Using pythag,

Hence,

^just subbing in AC

 

[ThatMathGuy]

Are the answers:

CD = 113.46 m

Bearing = 132 deg 41 min ?

Yeah, I don't think that's it. I agree with you for CD, but the bearing is wrong (I think). What you have to understand is the bearing is from North to the designated line, and usually North, would be, well, North, but in this case, its 3D trig, and north is actually not just UP. From your info, the line CA is going South and the line DA is going East. Therefore, the bearing from North to East is going to be 90 degrees because North and East meet at 90 degrees.

Do correct me if I'm wrong.

 

[ThatMathGuy]

Oh, and actually, I think the distance CD is 186.46 m

 

[braintic]

How do i post up graphs from microsoft word/geogebra?

Download 'Cute PDF'.