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

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

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

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

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 any triangle ABC, prove that cos A= frac{b^2+c^2-a^2}{2bc} .

In a triangleABC , prove by vector method that cos2A+cos2B+cos2Cge(-3)/(2) .

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