Hi guys have you ever heard the phrase you can’t unscramble an egg? In other word you
cannot go backwards. Well you cannot maybe able to do that in an egg but you can go backwards
with bearing what do I mean? In this particular question let us take a closer look we are
ask to find the bearing of O from A in other words we are going to go from here back to
here, and now what we are given is the bearing from here down to A in other word N O A the
bearing is 130 degrees. So we need to go backwards, the first thing we do when we here the magic
word “from” we need to draw in the diagram we need to draw in the crosses the north,
east, south, west. Now you probably heard me say before a problem well drawn is a problem
half solve. So let us draw in the cross word right over
here at A so got my trusty ruler here it is and I am going to draw in the crosses so we
can take a closer at this diagram. So let us draw the north south first of all – here
is our north south, and then across here we are just going to draw in the – east west—let
us put in there north ok there is our trusty crosses. Ok now let us put in the bearing,
now remember bearing are very important because they start at north and bearing are nothing
without north. Ok let us do that—and that is going to do clockwise all the way across
here back to up there. There is the bearing that we now out after, let us confirm this
from the question I will read the question, find the bearing of O—from A, so that means
the bearing going clockwise around that way, can you see that? – so let us take a closer
look because the most important thing is to look here that vertical line there because
we know the birth of bearing begin with north. So if we begin with north we have a parallel
lines if you notice there, we have a parallel line here, now the interesting thing is we
can actually incorporate some geometry in this which is great news because with geometry
we can actually find out what is bearing around there.
So first of all I wonder whether you notice that the angle, that if we get this angle
it is going to make the bearing so easy and that this angle right in there let me just
point it out in fact mark it out with the dot-- I wonder whether you can see why that
angle is so important that we get it because you know what? I wonder if you can see this.
If we get that, then we can work out the bearing why? Because the angle of illusion in other
words all the way around is 360 degrees, yeah? and if we take away that dot, that angle we
left with a bearing which is what we are after. So that is the good news, now let us go back
the geometry I mentioned earlier. Well we have a vertical line there north south we
have another vertical line here north south. Now when we have 2 parallel lines those it
make sense we can find angles system like corresponding angles, current area angles
and more importantly alternate that is seems to crop up in bearing quit commonly so let
us have a look here. If I want to find out what that angle is here that angle there see
that parallel line then that parallel line with that line we can actually find this angle
here couldn’t we? Let me mark that out those two angles are equal why? – alternate angles,
yeah? Alternate angles because can you see their head there? So they are equal all we
have to do is work out this angle and we will have that angle then take away from the revolution
and we left with the bearing. So let us do that process so what is this
angle? Well we know due to supplementary or straight lines angles that they are 180 degrees
let us put that in, so straight line – line angles = 180 degrees. Ok so take away 180
degrees all the way around and we are given 130 degrees all we have to do is subtract
the two and we are left with a red dot, yeah? so a 180 degrees take away what we have our
P is 130 let us do that take away 130 degrees that is going to give us the angle of red
dot, yeah? an angle in red dot is O here OA, yeah? that is what we are after. So 180 take
away 130 on the calculator or mentally, that equals a grand total the angle – right in
here – it is 180-130, 50 degrees let me mark it in the diagram 50 degrees, and now
if it is 50 degrees here it is also going to be because alternate angles are equal right
over here so that is also going to be 50 degrees – ok? Due to alternate angles so parallel
lines yields alternate – angles that little line <’s that means angle so we have given
our reasons we have totally justified it. Now our mission now is to work out what this
bearing is now becomes rather easy all we have to do is angle of revolution take away
50 and that will give us our bearing. So the bearing is revolution -- which is 360 degrees
and we take away this angles in there which is angle right there in the red dot so we
take away 50 degrees and that is going to give us a grand total of the bearing all the
ways around there which is 360 take away 50 on your calculator will give you – 310 degrees
let me mark it out right here all the way across there 310 that is the bearing let us
write in what that bearing is? That bearing A right there, the bearing --of O from A.
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