Solve

y+4y+20y=0,y(0)=2,y(0)=12\displaystyle {y}{''}+{4}{y}'+{20}{y}={0},\quad{y}{\left({0}\right)}=-{2},\quad{y}'{\left({0}\right)}={12}

y(t)\displaystyle {y}{\left({t}\right)} =