Sin cos tan homework

[gadgetgeek]

What should the formula be to work out the following question using sin, cos or tan? 28 years since doing this and totally forgotten.

A helicopter takes off from an army base on a bearing of 75deg and flies for 52km. How far east has the helicopt flown and how far north?

Once I can remember the workings I can help my son with the rest. Thk u.

[bibblebub]

52 cos (75°)

[Graham-W]

SOHCAHTOA
sine=Opposite/Hypotenuse
Cosine=Adjacent/Hypotenuse
Tan=Opposite/Adjacent

[gadgetgeek]

Nope, still not clear, sorry for being dense.

[pretty_snowdrop]

sohcahtoa...i think!!!!! sin=opp/hyp cos= adj/hyp and tan= opp/adj... so since you have an angle and one length you can work the other out.

[bibblebub]

have a look at this pic i've just done http://i39.tinypic.com/260ettk.png

[Buenchico]

Rough scribbles:
http://i39.tinypic.com/21d2xid.jpg

Chris

[Buenchico]

Ooh, there's posh, Bibblebub!

Much neater than my scribbles!
;-)

[old-wos-is-name]

Know what, this could be a foreign language to me now ( looks like my spelling has also gone that way) why should anyone need to know these things unless they are going to shoot a sam missle from the olympic stadium?

[gadgetgeek]

Thank you all. I still haven't a clue (and wish I had) but a light bulb moment has reached my son! Thank you. Night classes for me then!!!

[bibblebub]

but yours is much more explanatory Chris

[SeaJayPea]

Draw yourself a right-angled triangle with the right angle at the top left (North). You start from somewhere below this (South) with an angle of 75° and meet the horizontal (West-East) after 52 miles.

To find the distance to the East:

You know the angle, you know the length of the hypoteneuse and you're looking for the side opposite. So you finish up with Sin 75° = opp/hyp
opp = Sin 75° x 52 = 0.9659 x 52 = 50.2268

To find the distance to the north:

adj = cos 75° x 52 = 0.2588 X 52 = 13.4576

I think.

[Buenchico]

To be pedantic, Sophomoric, that's a mnemonic, rather than an acronym.

I always taught it as an acronym (Sohcahtoa) which I claimed to be the name of a volcanic island somewhere in the Far East!

[gadgetgeek]

Thks SeaJayPea, its starting to make sense to me. In what order do you type this into a calculator? Hope this is the last dumb question I have to ask! :-/

[gadgetgeek]

Buenchico, thank you for making me smile (that is smile not simile!!!) for the first time tonite.

[jake-the-peg]

If you look at a right angled triangle in such questions you will have one other angle ( here 75 degrees )

The longest side of a triangle is called the hypotenuse, the side nearest the angle you have is called the adjacent, the one opposite the angle is called just that.

draw it out and see which is which.

Now the sine of the angle you have is the opposite side divided by the hypotenuse

So you can multiply the hypotenuse by the sine on the angle to get the length of the adjacent side.

Here the helicopter has travelled 52 Km ( that's the Hypotenuse) so
52*sin(75) gives you the distance east

52*cos(75) gives you the distance North

Tan is a little trickier that's the opposite divided by the adjacent ( don't worry about that until you have cos and sine sorted)

Draw it out and try a few examples

Maths is like sex - you can't learn it from books only by doing it

[jocon]

Recommended website - Khan Academy. Really good, clear instructions on science subjects.

[Buenchico]

Different calculators use different methods, Gadgetgeek.


Basically, what you need to do is to find the sine of 75 degrees and then multiply it by 52. (Repeat with cosine).

Some calculators require you to press 'sin', '75', 'equals', 'times', '52', 'equals'
Others need '75', 'sin', 'times', '52', 'equals'.

Chris