With the help of vector method, prove that,`cosC=(a^2+b^2-c^2)/(2ab)`

With the help of vector method, prove that, cosA=(b^2+c^2-a^2)/(2bc)

With the help of vector method, prove that, cosB=(c^2+a^2-b^2)/(2ca)

Prove that, in any triangle ABC, cos C=(a^2+b^2-c^2)/(2ab) .

A, B, C and D are four points in space. Using vector methods, prove that AC^(2)+BD^(2)+AC^(2)+BC^(2)geAB^(2)+CD^(2) what is the implication of the sign of equality.

In DeltaABC, prove that cosA=(b^2+c^2-a^2)/(2b c) by vector method.

In any triangle ABC, then by vectors, prove that : c^2=a^2+b^2-2ab cos C .

In any triangle ABC, prove that : (cosA)/a+ (cosB)/b+(cosC)/c= (a^2+b^2+c^2)/(2abc) .