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Both the sine and the consine rule applies to any triangle, you do not necessary need a right angle!

You can usually use the cosine rule when you are given two sides and the included angle **(SAS)** or when you are given three sides and want to work out an angle** (SSS)**.

In order to use the sine rule, you need to know either two angles and a side **(ASA) **or two sides and a non-included angle **(SSA)**.

- Use the __ sine rule__ when a problem involves

- Use the
when a problem involves**cosine rule****three sides**and**one angle**

__The cosine equation:__

*a ^{2 }= b^{2} + c^{2}* -

(version given on formula sheet to find missing side)

(use this version for finding a missing angle)

__The sine equation:__

**a / sinA = b / sinB = c / sinC** (use to find the missing side)

**sinA / a = sinB / b = sinC / c** (use to find the missing angle)

**Key points to remember:**

__Sine Rule__:

- As you label the triangle, each side has the same letter as its opposite angle!
- If you are wanting to find the angle in the equation remember to use the sin
^{-1 }function on your calculator. - The greater the length is the greater is the opposite angle!

__Cosine Rule:__

- Remeber to use
**BIDMAS**when you work out the value on the right hand side for finding the missing side, hence put brackets around the (*2bc*cos (A) ).

One to one online tution can be a great way to brush up on your Maths knowledge.

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One to one online tution can be a great way to brush up on your Maths knowledge.

Have a Free Meeting with one of our hand picked tutors from the UK’s top universities

Find a tutor