# Thread: sin, cos, and tan

1. ## sin, cos, and tan

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!

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.

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

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

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

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.

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

4. Originally Posted by BsMummy
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?

Yep

Originally Posted by BsMummy

And does sin cos and tan only apply to right angle triangles?
Nope, there are many other applications. I was just guessing that you were looking at right angled triangles.

Originally Posted by BsMummy
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
Sort of makes sense.

you can only use Sine when you have the information on the opposite and hypotenuse sides. Likewise with the others as below.

5. THANKYOU SOOOOOO VERY MUCH

6. Originally Posted by BsMummy
And does sin cos and tan only apply to right angle triangles?
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.

7. Originally Posted by Matt Westwood
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.

We can solve a triangle that is not right-angled using the Sine and Cosine rules.

8. Well yes you can, but be careful about the context this question was being asked in! The SohCahToa formulae (which is what was being asked about) can only be used in right angled triangles.