Option C is correct. The law of cosines must be used to solve a triangle in the case of SAS rule (Side Angle Side Rule)
For a triangle, ABC with sides a, b, and c respectively, the law of cosines is used on such a triangle if there is a presence of an angle between any two sides.
[tex]c^2 = a^2 + b^2 + 2ab cos C[/tex]
Hence the law of cosines must be used to solve a triangle in the case of SAS rule (Side Angle Side Rule)
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