Use variation of parameters to find a particular solution, given the solutions y1,y2\displaystyle {y}_{{1}},{y}_{{2}} of the complementary equation

x2y4xy+(x2+6)y=x4\displaystyle {x}^{{2}}{y}{''}-{4}{x}{y}'+{\left({x}^{{2}}+{6}\right)}{y}={x}^{{4}}

y1=x2cos(x),y2=x2sin(x)\displaystyle {y}_{{1}}={x}^{{2}}{\cos{{\left({x}\right)}}},{y}_{{2}}={x}^{{2}}{\sin{{\left({x}\right)}}}

yp(x)=\displaystyle {y}_{{p}}{\left({x}\right)}=