Law of sines and cosines

Law of sines is basically the rule that says that sinA/a=sinB/b=SinC/c therefor they are all equal to eachother. This is used If given 2 sides and an opposite angle or if given 2 angles and an opposite side. The law of cosines states that a^2=b^2+c^2-2(c)(b)cosA;  b^2=a^2+c^2-2(a)(c)cosB;  c^2=b^2+a^2-2(a)(b)cosA. This is used when given 3sides or she given 2sides and an included angle. However, the law of cosines should only be used once per question because it is easy to make mistakes.