Trigonometry

[DelphiniumBlue]

Sin, cos, tan -what do they mean?I know you can use these to calculate an angle, but how? Revision guides don't make it clear.......
DS has an exam tomorrow on this, but hasn't been taught it( allegedly!)
Can anyone explain the basics? Please?

[mineofuselessinformation]

Does the school have a mymaths account?
He can log on, search for trig and then look at the online lesson.
It's a bit complicated to explain on here.

[PurpleDaisies]

They are ratios linking the length of particular sides of a right angles triangles to each other. As long as he can use them correctly he doesn't need to know where they come from.

[PurpleDaisies]

Sorry reread your question...BBC bite size should have a really clear guide. You can't explain it properly without drawing.

[BathshebaDarkstone]

Sine=opposite/hypotenuse
Cosine=adjacent/hypotenuse
Tangent=opposite/adjacent

Hope that helps.

[PurpleDaisies]

www.bbc.co.uk/schools/gcsebitesize/maths/geometry/trigonometryrev1.shtml

Is your son sitting the foundation or higher tier paper?

[DelphiniumBlue]

Year 9, hopefully will be higher tier in due course.
Thanks, you guys replied astonishingly quickly! have looked at bitesize but can't understand it.
Bathsheba, when you say for example that sine= opposite /hypotenuse, do you actually mean "is the same as"? Or that you use it to do something to the opposite side and the hypotenuse?
Thanks

[PurpleDaisies]

Ah, thought it was a GCSE. I hate to sound defeatist but in all likelihood if the test is tomorrow he's unlikely to get it before then. Is that the only topic on the test? Hopefully he'll be able to pick up marks on other questions, or the teacher will realise they haven't done a very good job teaching the class.

[DelphiniumBlue]

PurpleDaisies, I quite agree, but was hoping in desperation that someone might be able to put it in a nutshell of 2 sentences!
Pivot, thanks, we are using that and i think he is beginning to crack it after working through a few examples!
Thanks everyone, nice to know we are not alone! xx to the power of MN

[ragged]

There will be excellent videos on youtube explaining the basic trigonometric functions. Go look there.

[PurpleDaisies]

Sorry! It is quite a tricky topic that most students find tricky to grasp when they've just learnt it. YouTube might have some good videos, or could he try and see the teacher first thing? With a pen and paper it doesn't take too long to explain. Good luck anyway and sorry not to be more help.

[Stinkersmum]

I've not taught in the UK for a couple of years but trig in year 9? I wouldn't have thought it would've been taught yet.

[Stinkersmum]

Remember -finding lengths is standard function. Finding angles is inverse function.

[noblegiraffe]

Is he sitting a 6-8 SATs paper? If he hasn't been taught trig then he would be better off making sure he is solid on the stuff he has been taught rather than trying to master a tricky new topic last thing. The scho won't be expecting him to know trig if they haven't taught it! He can still get a level 8 without it too.

[throckenholt]

Probably too late for an exam today - but for what is worth :

With a right angled triangle (to start with) - each side has a name. The hypotenuse is the long side opposite the right angle. The opposite is the side opposite the angle you are interested in, and the one beside it is called the adjacent (for obvious reasons).

summary

You can use the lengths of the sides to find out the angle - you have to work out the ratio of the two sides, and then use a calculator to do the inverse function to find the angle itself.

The rules are shown here

If that doesn't make sense then you really need someone to go through it in person.

[DadDadDad]

Having just spent the last couple of weeks helping my DS prepare for his school maths exam, including trig, I fear it's a bit hopeless trying to help over the web like this in such a short timeframe!

For a start, he needs someone to sit down with his specific calculator, make sure it is set to degrees, and get him to practise just getting sin, cos and tan values out of it. (Older calculators, you would type [4] [0] [sin] to get the sine of 40 degrees; these days, they work with typing [sin] [4] [0] and you may need brackets.)

If he hasn't been taught it, why don't you take this up with his teacher? If he can't answer it, that's more of a reflection of the teacher than of him.