Yogi!!!!!!!!!!!!!!!!! (1 Viewer)

[chinkyeye]

yes, what is the sine rules?

 

[Muzzaw]

a/sine A = b/sine B = c/sine C

 

[Muzzaw]

^^^Sine rule.

Cosine rule:

c(squared) = a(squared) + b(squared) - 2ab * cosC

 

[chinkyeye]

can u beter explain it plz?

 

[Muzzaw]

Sorry mate, bit hard without diagrams.

There's an explanation of sine and cosine in the resources section.

 

[chinkyeye]

well...can u try and draw diagrms with the slash sing \ \ \ use that n draw 4 me?

 

[jnr_mafia]

jus remember 1 + 1 = 2

 

[Muzzaw]

Eeeerrrr, I think I'll give it a try with words.

Both are used when your trying to find either a side or an angle, but the difference is what the question gives you.

For sine rule, you'll be given either 2 angles and one side - so, you use:

a/sine A = b/sine B

E.g:

You have a triangle (not right angle - if they give you a right angled triangle then just use the trig. ratios), and the question asks you to find the length of side 'AZ'. If the triangle is labelled with another side (say, of length 20 cm) and two angles (let's say, 52 degrees and 63 degrees), and side AZ is opposite one of those angles (let's say that it's oppositte to 52 degrees) then you use sine rule, like this:

AZ/sine 52 = 20/sine 63

Therefore AZ = (20 * sine52)/sine 63.


With me?

 

[Muzzaw]

The other application of sine rule is to find angles.

In this case the question will give you 2 sides and an angle.

Rearrange the formula like so:

sine A/a = sine B/b

Now substitute into the formula.

E.g, you're asked to find the missing angle with the following data. 2 sides, one of which is 40 cm, and the other is 30 cm. One more angle is 60 degrees. Let's assume the missing angle is opposite 30 cm.

E.g

sine A/30 = sine 60/40

Therefore sine A = (30 * sine 60)/40

 

[Muzzaw]

Someone else wanna do cosine?

 

[PC]

Sine Rule to find a side:
side you're trying find over sine of the opposite angle = other side over sine of the opposite angle

Sine Rule to find an angle:
sine of the angle you're trying to find over the opposite side = sine of the other angle over sine of the opposite side

Cosine Rule to find a side:
one side squared plus other side squared minus two times first side times second side times cos of the angle in between them ... then remember to take the square root

Cosing Rule to find an angle:
one side square plus other side square minus opposite side squared all over two times the first times the second ... then remember to press [SHIFT] [COS]