The correct option is C \N
cot B+cot C−cot A=cos Bsin B+cos Csin C−cot A
=sin C cos B+cos C sin Bsin B sin C−cos A=sin(B+C)sinB sinC−cos Asin A
=sin2 A−sin B sin C cos Asin A sin B sin C=a2−bc cos Ak(abc)
Since=sinAa=sinBb=sinCc = k (say)
and cos A=b2+c2−a22bc=a2−bc(b2+c2−a2)2bc(abc)k
(a2−a2)abc K=0,{Asb2+c2−a22=3a2−a22=2a22=a2.}