Let #angleBAC=x#
let #A# be the area of #DeltaABC# #A=1/2*AB*AC*sinx#
we know that #sinx# has a maximum value of #1# ,
when #sinx=1, A# has the maximum value. #=> x=90^@#
and given #AB=AC=2011# cm #angleABC=ACB=45^@# #=> BCsin45=AB# #=> BC*1/sqrt2=2011# #=> BC=2011sqrt2# cm