Question 1034392
The angle of rotation of axes {{{theta}}} that would eliminate the xy term from the conic {{{Ax^2 +Bxy +Cy^2 + Dx + Ey +F = 0 }}}is 

{{{cot(2*theta) = (A - C)/B}}}.

==> {{{cot(2*theta) = (A - C)/B = (3-3)/1 = 0}}}.

==> {{{tan(2*theta) = infinity}}}  ==> {{{2*theta = 90^o}}}  ==> {{{highlight(theta = 45^o)}}}.