Please explain me to understand the solution: Horizontal garden ABCD (trapezium) with AB parallel to DC

[Laia]

Hello, can someone explain why do they subtract 78 from 270? I thought it needs to be subtracted from 360. I've attached the question and marking scheme. Also, there's another problem that I do not understand, it's also a bearing problem so please help me understand these.

 

[khansaheb]

Hello, can someone explain why do they subtract 78 from 270? I thought it needs to be subtracted from 360. I've attached the question and marking scheme. Also, there's another problem that I do not understand, it's also a bearing problem so please help me understand these.

According to your class-notes/textbook:

What is the definition of "bearing" angle and how is it reported?

 

[Laia]

According to your class-notes/textbook:

What is the definition of "bearing" angle and how is it reported?

As far as I've understood, to find the bearing angle, I need to built up a north pole line.

 

[khansaheb]

As far as I've understood, to find the bearing angle, I need to built up a north pole line.

Correct - did you do that? Did you construct an East line and South line and a West line?

From your sketch, please show us the location (and direction) of the bearing angle (from A to D).

 

[Laia]

No I haven't because I don't know where to start so I watched the marking scheme but still didn't understand of why it has to be subtracted from 270

 

[khansaheb]

No I haven't because I don't know where to start so I watched the marking scheme but still didn't understand of why it has to be subtracted from 270

According to your sketch, which angle (in terms of A,B,C & D as shown in the OP) is "it" ?

 

[Laia]

Oh it means the angle 78. I don't understand why the angle 78 has subtracted from 270. Can you point out why it has to do like that?

 

[khansaheb]

Oh it means the angle 78. I don't understand why the angle 78 has subtracted from 270. Can you point out why it has to do like that?

Which angle is 78? Please name it using the points given in the sketch.

 

[Laia]

The angle ADC is 78°

 

[khansaheb]

The angle ADC is 78°

Correct.... now draw a sketch (including the given A, B, C & D) of NESW with the origin at A.

Then think about the relationship between the bearing angle of D from A - and the calculated angle(ADC=78).

 

[Laia]

Is it like this? I now know why I was stuck. Because I drew the north pole from D by mistake. After drawing the north pole at A, I did another mistake which was finding the bearing by anti clockwise without noticing but I quickly noticed it and finally get to the answer I want. thank you very much for helping me!