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

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)

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

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

Without expanding the determinant, prove that |[a,a^2,bc],[b,b^2,ca],[c,c^2,ab]| = |[1,a^2,a^3],[1,b^2,b^3],[1,c^2,c^3]|

If A,B,C are the angles of a triangle then prove that cosA+cosB-cosC=-1+4cos(A/2)cos(B/2)sin(C/2)