(adsbygoogle = window.adsbygoogle || []).push({}); Cosine Rule , what good is it ????

Does the Cosine rule hold true for say negative lengths ??? as in a vector quantity like displacement ???

I came across this problem which had -15km and 10km as the known sides whereas the angle opposite the unkown side is 60 degree ....

I tries using c^2 = a^2 + b^2 - 2*a*b cosC but this didnt work .... then on account of frustration i forcibly changed the '-' part of the formula to a '+' only to find that it works ... ???

Can someone explain this to me ??

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# Cosine Rule , what good is it ?

**Physics Forums | Science Articles, Homework Help, Discussion**