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(GCSE) Sine, Cosine Rule

Hey, Just wondering if anyone had any ways of remembering when to use the sine and cosine rules, I know they are not for right angled triangles, Its just remembering when to use each one?

Any help is appreciated. :smile:

Reply 1

Maqdah

8

Just memorise them. They are pretty easy. To memorise them easily, keep answering questions that require you to use the rules :smile:

Reply 2

Diaz

OP

12

Maqdah

Just memorise them. They are pretty easy. To memorise them easily, keep answering questions that require you to use the rules :smile:

I know what your saying, its just when I get to past papers I have no idea which one to use.

Reply 3

icapturethecastle

16

u'll be able to work out which ones to use
if one doesn't work it'll be the other one :wink:

Reply 4

qgujxj39

17

I don't know how I remember the cosine rule. I think I just started reciting "cos A equals b squared plus c squared take a squared all over two b c" for a few minutes one day, and it just stuck. One way which helps to remember which letters to put where is that the cosine rule still holds if you interchange the b and c, whereas the a can't because it is the "odd one out" as it corresponds to the angle. I'm not too good at articulating that, but it makes sense to me :p:

The sine rule is much easier to remember.

Reply 5

Sports Racer

14

You can usually *see* when to use each.

Trust me, just memorising when to use each (eg "Oh yes, I use the Sine rule when you're given to angles blah blah") will not be that useful. Practice will give you a better indication. And as tam.tam says, if one doesn't work, try the other!

Although I can give you one thing to learn. As the Cosine rule only deals with one angle, you can probably determine that it's a pretty safe bet that if you're given two angles and a side, the Sine is the one to go for.

Reply 6

Diaz

OP

12

tam.tam

u'll be able to work out which ones to use
if one doesn't work it'll be the other one :wink:

Oh yeah, So I don't actually have to memorise them, just use one then if that don't work I use the other one!
Thank you +rep

Reply 7

Maqdah

8

ooooooooo ok. I sometimes face the same problem, do what I do:

Write both equations in the corner
write everything given underneath and then determine which is better to find the answer.

OR

You could memorise this:

Sin rule is used to find an unknown length when you know two angles and an opposite side or vice versa (two length and opposite angle are know)

For the cos rule to find an unknow side of the triangle knowing 2 sides or the triangle and the angle between those 2 sides. You could also use it to find the angle of any side knowing the length of the 3 sides.

Reply 8

Diaz

OP

12

Sports Racer

You can usually *see* when to use each.

Trust me, just memorising when to use each (eg "Oh yes, I use the Sine rule when you're given to angles blah blah") will not be that useful. Practice will give you a better indication. And as tam.tam says, if one doesn't work, try the other!

Although I can give you one thing to learn. As the Cosine rule only deals with one angle, you can probably determine that it's a pretty safe bet that if you're given two angles and a side, the Sine is the one to go for.

Thanks for that also! :biggrin:

Reply 9

ryukk

17

Original post by Diaz

Hey, Just wondering if anyone had any ways of remembering when to use the sine and cosine rules, I know they are not for right angled triangles, Its just remembering when to use each one?

Any help is appreciated. :smile:

this is really 10 years old!

Reply 10

TheOnlyOne999

7

Original post by miss_ambitious

this is really 10 years old!

11 years old now lmfao

Reply 11

MADHUMOHAN

1

The Sine rule is used when we are given either two angles and one side (or) Two sides and a non included angleThe Cosine rule is used when we are given either Three sides (or) Two sides and the included angle

Reply 12

davros

16

Original post by MADHUMOHAN

The Sine rule is used when we are given either two angles and one side (or) Two sides and a non included angleThe Cosine rule is used when we are given either Three sides (or) Two sides and the included angle

This is a 12-year-old thread you're replying to!! :biggrin:

(GCSE) Sine, Cosine Rule

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