Cosine rule

Cosine rule – We can use the cosine formula to find the length of a side or the size of an angle.

Sine and Cosine are used to find the angle of a shape

`a^2=b^2+c^2-2bc\cosA`

The following mnemonic (picture memory aid) is what we recommend to remember this formula.

Some calculations don’t require the Cosine rule

Zero

That’s correct. We recommend nothing. We recommend that you do not remember this formula. You don’t need it.

See examples NOT using cosine rule.