If a `cos A =b cos B, ` then the triange is

If a cos A=b cos B , then the triangle ,is

If three angles A, B, C are such that cos A+ cos B + cos C = 0 and if lambda cos A cos B cos C = cos 3A + cos 3B + cos 3C , then value of lambda is :

cos(A + B) cos (A-B) =

Prove that : cos (A - B) = cos A cos B + sin A sin B .

Prove that : cos (A + B) = cos A cos B - sin A sin B .

if ( cos A + cos B )/( sin A + sin B ) = k ( (sin A - sin B)/ ( cos A- cos B)) then k is

If in right angled triange ABC,angle B is right angle and tan A=1, then the value 2sin A cos A will be

If sin A+sin B=a and cos A+cos B=b then cos (A+B)=