Im having real troubles with understanding when to use sin, cos and tan - i know how to find them but don't know which ones to use and when!

Maths has never been a good subject of mine! so i aplogise if this is a silly question!

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- Sep 9th 2009, 08:43 PM #1

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- Sep 9th 2009, 09:01 PM #2
Not a silly question.

I assume you are talking about right angled triangles?

If so, you must firstly and most importantly know how to label the sides of the triangle in relation to the angle in question. If that is not a problem consider the trigonometric ratios.

$\displaystyle \sin(\theta) = \frac{O}{H}$

$\displaystyle \cos(\theta) = \frac{A}{H}$

$\displaystyle \tan(\theta) = \frac{O}{A}$

To decide which raiot to use inspect your triangle. If it has information on sides O and H then employ sine. When I say information, this could be a value or an unknown.

- Sep 9th 2009, 09:06 PM #3

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Thankyou for your reply

so i understand the sohcahtoa bit and when u say inspect the triangles and its side and whether it has a value or not - if it has now value and has a x or a ? instead that is still counted as a value am i correct?

And does sin cos and tan only apply to right angle triangles?

Also inregards to opposite and adjacent and hypotenuse - are they paired up with any of the sin cos or tans? not sure if that one makes sense

- Sep 9th 2009, 09:21 PM #4

- Sep 9th 2009, 09:35 PM #5

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- Sep 9th 2009, 10:04 PM #6
Just to reduce confusion (sorry to contradict you pickslides):

In this context YES. That is, you can't use sin, cos and tan if the triangle you are looking at does *NOT* have a right angle in it.

What you can do though is split the triangle into two right angle triangles by drawing a line inside it. This will be more advanced stuff though, you'll be better off sticking with the simple stuff for now till you get the hang of it.

- Sep 10th 2009, 02:18 PM #7

- Sep 10th 2009, 09:41 PM #8