Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 3 - No. 16)

In a non-right angled triangle, with sides a,b and c and the angles opposite them A, B and C, which formula represents the cosine rule correctly?

a²=b²+c²-2bc cos A

a² = b²-c²-2bc cos A

a²=b²-c²+2bc cos A

a²=b²+c²+2bc cos A

This is the correct formula of the Cosine rule.