Using vector method prove that in any triangle `ABC a^2=b^2+c^2-2bc cos A`.

Using vectors , prove that in a triangle ABC a^(2)= b^(2) + c^(2) - 2bc cos A where a,b,c are lengths of the ideas opposite to the angles A,B,C of triangle ABC respectively .

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

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

Prove the following by vector method. in any triangle ABC, a = bcosC+c cosB.

Prove by vector method that in a Delta ABC, c^(2) = a^(2) + b^(2) - 2ab cos C .

Using vector method prove that cosA=(b^2+c^2-a^2)/(2bc)

Prove that in any triangle ABC(i) c^(2)=a^(2)+b^(2)-2ab cos C( ii) c=b cos A+a cos B

Using vector method in a triangle , prove that, (ii) cos A = (b^2+c^2-a^2)/(2bc) .

Cosine formula: With usual notations in any triangle ABC Prove that : cos A= (b^(2)+c^(2)-a^(2))/(2bc) .